{"id":34196,"date":"2017-05-23T06:00:29","date_gmt":"2017-05-23T06:00:29","guid":{"rendered":"https:\/\/wp.lvh.me\/blog\/2017\/05\/23\/what-is-an-anti-spam-system-how-can-it-block-an-email\/"},"modified":"2026-10-15T16:36:57","modified_gmt":"2026-10-15T16:36:57","slug":"what-is-an-anti-spam-system-how-can-it-block-an-email","status":"publish","type":"post","link":"https:\/\/mailrelay.com\/en\/blog\/2017\/05\/23\/what-is-an-anti-spam-system-how-can-it-block-an-email\/","title":{"rendered":"What are anti-spam systems? How to tell if your IP is on a spam blacklist"},"content":{"rendered":"

In this post we want to go over which anti-spam systems<\/strong> and other checks are taken into account when deciding whether an email send is spam and can cause our newsletters to be blocked<\/strong>.<\/p>\n

<\/p>\n

You probably already know many of them, such as the well-known blacklists<\/strong>, but others may be new to you, and with this article you’ll be able to keep them in mind when identifying possible problems with your newsletters.<\/p>\n

We’ll go through them one by one, in the order in which they can block<\/strong> or let through an email marketing send.<\/p>\n

Let’s get started.<\/p>\n\n

\u00b7 Queuing<\/h2>\n

It could be called a temporary block based on reputation<\/strong> rather than on spam, since it doesn’t actually do any analysis of that kind. Instead, it looks at empirical data from previous sends and lets messages through, or not, depending on the reputation those previous sends have built up.<\/strong><\/p>\n

Bear in mind, however, that sending spam will make queuing increase very sharply.<\/p>\n

Queuing is basically when an ISP or hosting provider only lets in a certain number of messages per hour from the same sender or IP<\/strong>.<\/p>\n

For the rest, it asks for the send to be retried later<\/strong> by the server that is sending them.<\/p>\n

When this happens, the messages that exceed this quota are put in a queue to be retried later, hence the name queuing.<\/p>\n

They will be retried a certain number of times, according to the period configured on the sending server, and once that period is over they will be discarded.<\/p>\n

In these articles we take a very thorough look at queuing and how to avoid it:<\/p>\n

    \n
  1. Why do some email sends get queued?<\/a><\/li>\n
  2. Rejections by ISPs due to sending volume<\/a><\/li>\n<\/ol>\n

    Let’s carry on<\/p>\n

    \u00b7 Robinson lists<\/h2>\n

    The name comes from Daniel Defoe<\/strong>‘s famous character and tries to capture what these lists aim to achieve: an isolation from advertising similar to that of the famous castaway.<\/p>\n

    It isn’t a spam-blocking method<\/strong> as such, since it works passively rather than actively.<\/p>\n

    Nor is it related to email blacklists, even though the name is somewhat similar.<\/p>\n

    They are associations that ESPs can join<\/strong>, committing never to send advertising emails to their members, even if the ESP’s customers have them in their databases.<\/p>\n

    They present themselves as advertising opt-out services and are designed so that users who want to avoid receiving commercial emails of any kind can sign up for them.<\/p>\n

    And be sure that the affiliated email marketing providers and companies won’t send them any advertising newsletters.<\/p>\n

    \"Illustration<\/p>\n

    \u00b7 SPF block<\/h2>\n

    It’s the most common, and the first, of the actual blocks your newsletter can run into.<\/p>\n

    But it isn’t related to blacklists, IPs or blacklisted domains either<\/p>\n

    It simply blocks or penalizes messages that come from IPs not authorized<\/strong> in the SPF record<\/a>.<\/p>\n

    In these articles you can find more information on how it works and how to configure your sender properly so you don’t run into any problems:<\/p>\n

      \n
    1. What is SPF?<\/a><\/li>\n<\/ol>\n

      \u00b7 RBLs or blacklists: what email blacklists are and how they work<\/h2>\n

      These blocking systems are a little more involved.<\/p>\n

      RBL is an acronym for “Real-time Blackhole List<\/strong>“, the name of the first system in the IT world to create a list for blocking sends from senders included on it.<\/p>\n

      \u25ba What are spam blacklists?<\/h3>\n

      They are companies, associations or even individual users who share a list of IPs or senders they have received spam complaints about<\/strong> or that have been detected as spam on their servers.<\/p>\n

      Some are free and others are paid, and mail server administrators can enable them so that, if a message arrives from an IP or sender on their lists, it goes to spam or is even blocked completely.<\/p>\n

      They have evolved into different types of lists, adding (besides senders or IPs) checks on DNS servers, open SMTP servers, whether the sender has the abuse and postmaster accounts set up, and so on.<\/p>\n

      \u25ba How to tell if your IP is on a blacklist<\/h3>\n

      There are hundreds of blacklists in total.<\/strong><\/p>\n

      So checking them manually can be impossible.<\/p>\n

      However, there are websites that can check multiple blacklists at once.<\/p>\n

      For example, on this website you can check whether an IP or domain is on any of them:<\/p>\n

      https:\/\/multirbl.valli.org\/<\/p>\n

      That said, the vast majority are irrelevant, and only the biggest ones tend to be used by mail servers and anti-spam systems, for example:<\/p>\n

        \n
      1. Barracuda Networks:<\/strong> barracudacentral.org<\/a><\/li>\n
      2. Spamcop:<\/strong> bl.spamcop.net<\/a><\/li>\n
      3. Spamhaus:<\/strong> sbl-xbl.spamhaus.org<\/a><\/li>\n
      4. URIBL:<\/strong> uribl.com<\/a><\/li>\n<\/ol>\n

        If you’re on one of these, you do need to take action to fix it.<\/p>\n

        \"How<\/p>\n

        \u00b7 Greylists<\/h2>\n

        A consequence of the previous ones.<\/p>\n

        Greylists were introduced to deal with false positives and doubtful alerts.<\/p>\n

        What they do is quarantine a send from a specific sender or IPs, not permanently: they ask for delivery retries to be postponed for a few hours.<\/p>\n

        Others work the same way but based on a certain number of spam complaints. If that number isn’t exceeded during the quarantine hours, the sender is removed from the greylist.<\/p>\n

        \u00b7 Spamtraps<\/h2>\n

        An unusual anti-spam system. It consists of spreading trap email accounts around, for example on the contact pages of websites, in business directories, and so on.<\/p>\n

        If someone sends newsletters to those accounts, we know they obtained them without complying with anti-spam regulations and that they are sending unsolicited emails.<\/p>\n

        Once these sends are detected, we get added to blacklists or blocked from a particular ISP. In this article we take a closer look at spamtraps and how they work:<\/p>\n

        What are spamtraps?<\/a><\/p>\n

        \u00b7 IP reputation systems<\/h2>\n

        The best known is www.senderscore.org<\/a>, which belongs to Returnpath.<\/p>\n

        They are services that give a score to IPs or IP ranges based on the spam complaints received about sends from them, changes in sending volume, and sends to spamtraps.<\/p>\n

        ISPs like Hotmail or Gmail and hosting providers have their own internal evaluation systems<\/strong> for this.<\/p>\n

        When a block happens for this reason, it usually comes as a soft bounce<\/strong>, giving the sender the chance to take corrective action and be able to send in the future.<\/p>\n

        \u00b7 Server-side anti-spam systems<\/h2>\n

        Corporate servers and hosting providers usually enable server-level anti-spam systems that filter every message before delivering it to the recipients’ accounts.<\/p>\n

        They tend to be an intermediate layer between blocks for SPF or for being listed on the main RBLs and the local anti-spam filters we’ll look at later.<\/p>\n

        There are paid systems such as Spamtitan<\/strong> or Spamina<\/strong> (they usually offer extras like reports and dashboards for users) and free systems such as SpamAssassin<\/strong> (see the box of the same name).<\/p>\n

        The reason RBLs, SPF and other blocking systems are checked first is to get rid of the junk before messages are passed to the server’s local anti-spam filter<\/strong>.<\/p>\n

        Only the messages that haven’t already been discarded reach it, and this matters for two reasons: first, some systems are paid and charge by the number of messages analyzed; and second, they consume significant server resources, since the local anti-spam filter performs a much more complex analysis than the blocking systems we’ve seen so far.<\/p>\n

        Specifically, what they do is generate a spamscore<\/strong> by analyzing not only the reputation of the sending IP and domain and whether they appear on various blacklists and reputation systems.<\/p>\n

        But also the content of the message design, penalizing it for various reasons, usually related to looking like spammers’ designs, and adding an extra score from intelligent or, in their jargon, Bayesian systems, based on previous analyses of similar messages across their user network.<\/p>\n

        This article has more information on how it works and what spamscore is:<\/p>\n

        What is spamscore?<\/a><\/p>\n

        \n
        SpamAssassin<\/div>\n
        \n

        Created in 1997 and part of the Apache Software Foundation since 2004, it is the most widely used open-source server-side anti-spam system, especially in B2B environments.<\/p>\n

        It has more than 700 rules that add or subtract points based on the design, RBLs, sender configuration, and so on.<\/p>\n

        These make up the message’s spamscore, and the message is let through or blocked depending on the score threshold set by the user or administrator.<\/p>\n

        It’s a very good way to check whether your newsletter could end up as spam<\/strong> in an email campaign. In fact, the report system in the Mailrelay panel uses SpamAssassin to produce its reports.<\/p>\n

        SpamAssassin on Wikipedia<\/a><\/p>\n

        SpamAssassin<\/a><\/p>\n<\/div>\n<\/div>\n

        \"How<\/p>\n

        \u00b7 Intelligent or social B2C anti-spam<\/h2>\n

        B2C ISPs like Hotmail, Gmail and others use blacklists and reputation lists, SPF checks and spamscore measurements similar to the server-side anti-spam systems we’ve just seen.<\/p>\n

        But then they add an extra layer of control that we could call social detection of unsolicited bulk newsletters.<\/p>\n

        For sends that pass all the previous checks, it analyzes how the subscribers who received them interact with them, and blocks the send or lowers its reputation if, for example, too many of them click the “this is spam” button<\/strong>, or most of them don’t view it or click on it and delete it straight away.<\/p>\n

        One example is Microsoft’s SmartScreen filter<\/strong>:<\/p>\n

        https:\/\/en.wikipedia.org\/wiki\/Microsoft_SmartScreen<\/a><\/p>\n

        One of its components does this work to block sends in real time in Outlook and Hotmail<\/strong>.<\/p>\n

        And that last part is important: in real time.<\/strong><\/p>\n

        In other words, a bulk send that initially has no problems with blacklists, spamscore or other blocks may be delivered correctly at the start of the send.<\/p>\n

        And then, before it’s complete:<\/em><\/p>\n

        It may go to the spam folder or be blocked because of the interaction or lack of it<\/strong> from the subscribers who have been receiving it, or because they have been marking it<\/strong> as spam.<\/p>\n

        \u00b7 Local desktop anti-spam<\/h2>\n

        The last barrier, and one we can’t get any feedback from, is the local anti-spam filter<\/strong> the recipient may have installed on their computer.<\/p>\n

        If they use a desktop email client such as Outlook or Thunderbird<\/strong>, they may use its anti-spam rules or the email add-on of one of the most popular antivirus programs.<\/p>\n

        These add-ons use the systems we’ve just seen, so a final block on their part is unlikely if all the previous checks have been passed.<\/p>\n

        \u00b7 Summary, detecting a block and conclusion (don’t panic)<\/h2>\n

        To finish, here’s a quick recap of the points where a newsletter can be blocked, either because it’s detected as spam or indirectly because spam or unsolicited newsletters have been sent:<\/p>\n

          \n
        1. Queuing<\/li>\n
        2. Robinson lists<\/li>\n
        3. SPF block<\/li>\n
        4. RBLs or blacklists<\/li>\n
        5. Greylists<\/li>\n
        6. Spamtraps<\/li>\n
        7. IP reputation systems<\/li>\n
        8. Server-side anti-spam system<\/li>\n
        9. Intelligent or social B2C anti-spam<\/li>\n
        10. Local desktop anti-spam<\/li>\n<\/ol>\n

          We’ve listed them in the order in which a newsletter may encounter and pass them, but this shouldn’t be taken as a linear system.<\/p>\n

          In fact, many of these systems are combined into a single block, like server-side anti-spam systems, which use several of the points we’ve covered.<\/p>\n

          Nor does passing one of them guarantee that the others won’t block us.<\/strong><\/p>\n

          So how can we check whether we’re being blocked?<\/strong> As a general rule, if the anti-spam report for the design in the Mailrelay panel doesn’t show any problems.<\/p>\n

          And the newsletter also reaches the public ISPs correctly, it’s almost certain that we’re not being blocked, since between them they use practically all the checkpoints we’ve covered.<\/p>\n

          If there are delivery problems,<\/strong> to find out where the problem might be, besides the panel’s spam report, you need to check the response the destination server is giving, since it often states the reason for the block.<\/p>\n

          You can do this from the panel under Sent<\/strong> \u2013 Search logs<\/strong>, or by asking support to look into it.<\/p>\n

          As we’ve seen, there are many systems for blocking spam, but don’t panic, hitchhikers.<\/strong><\/p>\n

          These blocks are very unlikely if we send properly and follow the sending rules:<\/p>\n

            \n
          1. Tips to keep your newsletter from being considered spam<\/a><\/li>\n
          2. Double opt-in sign-ups<\/a><\/li>\n<\/ol>\n

            \"No\u00e9<\/a><\/p>\n

            All these filters are directly related to your sender reputation<\/a>, a key factor in getting your emails into the inbox.<\/p>\n","protected":false},"excerpt":{"rendered":"

            In this post we want to go over which anti-spam systems and other checks are taken into account when deciding whether an email send is spam and can cause our newsletters to be blocked.<\/p>\n","protected":false},"author":7,"featured_media":15594,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"_uag_custom_page_level_css":"","footnotes":""},"categories":[882,562],"tags":[],"class_list":["post-34196","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-deliverability-and-technical-aspects","category-email-marketing-2"],"yoast_head":"\nAnti-Spam Systems: What They Are and How to Tell If You're Blacklisted<\/title>\n<meta name=\"description\" content=\"Mailrelay explains what anti-spam systems are and the types that exist, such as Robinson lists, anti-spam systems and block detection. Only here!\" \/>\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<link rel=\"canonical\" href=\"https:\/\/mailrelay.com\/en\/blog\/2017\/05\/23\/what-is-an-anti-spam-system-how-can-it-block-an-email\/\" \/>\n<meta property=\"og:locale\" content=\"en_US\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"Anti-Spam Systems: What They Are and How to Tell If You're Blacklisted\" \/>\n<meta property=\"og:description\" content=\"Mailrelay explains what anti-spam systems are and the types that exist, such as Robinson lists, anti-spam systems and block detection. Only here!\" \/>\n<meta property=\"og:url\" content=\"https:\/\/mailrelay.com\/en\/blog\/2017\/05\/23\/what-is-an-anti-spam-system-how-can-it-block-an-email\/\" \/>\n<meta property=\"og:site_name\" content=\"Mailrelay\" \/>\n<meta property=\"article:publisher\" content=\"https:\/\/www.facebook.com\/Mailrelay\/\" \/>\n<meta property=\"article:published_time\" content=\"2017-05-23T06:00:29+00:00\" \/>\n<meta property=\"article:modified_time\" content=\"2026-10-15T16:36:57+00:00\" \/>\n<meta property=\"og:image\" content=\"https:\/\/mailrelay.com\/wp-content\/uploads\/2017\/04\/sistemas-antispam.jpg\" \/>\n\t<meta property=\"og:image:width\" content=\"630\" \/>\n\t<meta property=\"og:image:height\" content=\"340\" \/>\n\t<meta property=\"og:image:type\" content=\"image\/jpeg\" \/>\n<meta name=\"author\" content=\"No\u00e9 Soriano\" \/>\n<meta name=\"twitter:card\" content=\"summary_large_image\" \/>\n<meta name=\"twitter:creator\" content=\"@mailrelay\" \/>\n<meta name=\"twitter:site\" content=\"@mailrelay\" \/>\n<meta name=\"twitter:label1\" content=\"Written by\" \/>\n\t<meta name=\"twitter:data1\" content=\"No\u00e9 Soriano\" \/>\n\t<meta name=\"twitter:label2\" content=\"Est. reading time\" \/>\n\t<meta name=\"twitter:data2\" content=\"9 minutes\" \/>\n<script type=\"application\/ld+json\" class=\"yoast-schema-graph\">{\"@context\":\"https:\\\/\\\/schema.org\",\"@graph\":[{\"@type\":\"Article\",\"@id\":\"https:\\\/\\\/mailrelay.com\\\/en\\\/blog\\\/2017\\\/05\\\/23\\\/what-is-an-anti-spam-system-how-can-it-block-an-email\\\/#article\",\"isPartOf\":{\"@id\":\"https:\\\/\\\/mailrelay.com\\\/en\\\/blog\\\/2017\\\/05\\\/23\\\/what-is-an-anti-spam-system-how-can-it-block-an-email\\\/\"},\"author\":{\"name\":\"No\u00e9 Soriano\",\"@id\":\"https:\\\/\\\/mailrelay.com\\\/en\\\/#\\\/schema\\\/person\\\/015806c54f5ded021ad304cd2e1b8c1d\"},\"headline\":\"What are anti-spam systems? How to tell if your IP is on a spam blacklist\",\"datePublished\":\"2017-05-23T06:00:29+00:00\",\"dateModified\":\"2026-10-15T16:36:57+00:00\",\"mainEntityOfPage\":{\"@id\":\"https:\\\/\\\/mailrelay.com\\\/en\\\/blog\\\/2017\\\/05\\\/23\\\/what-is-an-anti-spam-system-how-can-it-block-an-email\\\/\"},\"wordCount\":2025,\"publisher\":{\"@id\":\"https:\\\/\\\/mailrelay.com\\\/en\\\/#organization\"},\"image\":{\"@id\":\"https:\\\/\\\/mailrelay.com\\\/en\\\/blog\\\/2017\\\/05\\\/23\\\/what-is-an-anti-spam-system-how-can-it-block-an-email\\\/#primaryimage\"},\"thumbnailUrl\":\"https:\\\/\\\/mailrelay.com\\\/wp-content\\\/uploads\\\/2017\\\/04\\\/sistemas-antispam.jpg\",\"articleSection\":[\"Deliverability and Technical Aspects\",\"email marketing\"],\"inLanguage\":\"en-US\"},{\"@type\":\"WebPage\",\"@id\":\"https:\\\/\\\/mailrelay.com\\\/en\\\/blog\\\/2017\\\/05\\\/23\\\/what-is-an-anti-spam-system-how-can-it-block-an-email\\\/\",\"url\":\"https:\\\/\\\/mailrelay.com\\\/en\\\/blog\\\/2017\\\/05\\\/23\\\/what-is-an-anti-spam-system-how-can-it-block-an-email\\\/\",\"name\":\"Anti-Spam Systems: What They Are and How to Tell If You're Blacklisted\",\"isPartOf\":{\"@id\":\"https:\\\/\\\/mailrelay.com\\\/en\\\/#website\"},\"primaryImageOfPage\":{\"@id\":\"https:\\\/\\\/mailrelay.com\\\/en\\\/blog\\\/2017\\\/05\\\/23\\\/what-is-an-anti-spam-system-how-can-it-block-an-email\\\/#primaryimage\"},\"image\":{\"@id\":\"https:\\\/\\\/mailrelay.com\\\/en\\\/blog\\\/2017\\\/05\\\/23\\\/what-is-an-anti-spam-system-how-can-it-block-an-email\\\/#primaryimage\"},\"thumbnailUrl\":\"https:\\\/\\\/mailrelay.com\\\/wp-content\\\/uploads\\\/2017\\\/04\\\/sistemas-antispam.jpg\",\"datePublished\":\"2017-05-23T06:00:29+00:00\",\"dateModified\":\"2026-10-15T16:36:57+00:00\",\"description\":\"Mailrelay explains what anti-spam systems are and the types that exist, such as Robinson lists, anti-spam systems and block detection. Only here!\",\"breadcrumb\":{\"@id\":\"https:\\\/\\\/mailrelay.com\\\/en\\\/blog\\\/2017\\\/05\\\/23\\\/what-is-an-anti-spam-system-how-can-it-block-an-email\\\/#breadcrumb\"},\"inLanguage\":\"en-US\",\"potentialAction\":[{\"@type\":\"ReadAction\",\"target\":[\"https:\\\/\\\/mailrelay.com\\\/en\\\/blog\\\/2017\\\/05\\\/23\\\/what-is-an-anti-spam-system-how-can-it-block-an-email\\\/\"]}]},{\"@type\":\"ImageObject\",\"inLanguage\":\"en-US\",\"@id\":\"https:\\\/\\\/mailrelay.com\\\/en\\\/blog\\\/2017\\\/05\\\/23\\\/what-is-an-anti-spam-system-how-can-it-block-an-email\\\/#primaryimage\",\"url\":\"https:\\\/\\\/mailrelay.com\\\/wp-content\\\/uploads\\\/2017\\\/04\\\/sistemas-antispam.jpg\",\"contentUrl\":\"https:\\\/\\\/mailrelay.com\\\/wp-content\\\/uploads\\\/2017\\\/04\\\/sistemas-antispam.jpg\",\"width\":630,\"height\":340},{\"@type\":\"BreadcrumbList\",\"@id\":\"https:\\\/\\\/mailrelay.com\\\/en\\\/blog\\\/2017\\\/05\\\/23\\\/what-is-an-anti-spam-system-how-can-it-block-an-email\\\/#breadcrumb\",\"itemListElement\":[{\"@type\":\"ListItem\",\"position\":1,\"name\":\"Home\",\"item\":\"https:\\\/\\\/mailrelay.com\\\/en\\\/\"},{\"@type\":\"ListItem\",\"position\":2,\"name\":\"What are anti-spam systems? How to tell if your IP is on a spam blacklist\"}]},{\"@type\":\"WebSite\",\"@id\":\"https:\\\/\\\/mailrelay.com\\\/en\\\/#website\",\"url\":\"https:\\\/\\\/mailrelay.com\\\/en\\\/\",\"name\":\"Mailrelay\",\"description\":\"Mailrelay.com - Email Marketing Software\",\"publisher\":{\"@id\":\"https:\\\/\\\/mailrelay.com\\\/en\\\/#organization\"},\"potentialAction\":[{\"@type\":\"SearchAction\",\"target\":{\"@type\":\"EntryPoint\",\"urlTemplate\":\"https:\\\/\\\/mailrelay.com\\\/en\\\/?s={search_term_string}\"},\"query-input\":{\"@type\":\"PropertyValueSpecification\",\"valueRequired\":true,\"valueName\":\"search_term_string\"}}],\"inLanguage\":\"en-US\"},{\"@type\":\"Organization\",\"@id\":\"https:\\\/\\\/mailrelay.com\\\/en\\\/#organization\",\"name\":\"Mailrelay\",\"url\":\"https:\\\/\\\/mailrelay.com\\\/en\\\/\",\"logo\":{\"@type\":\"ImageObject\",\"inLanguage\":\"en-US\",\"@id\":\"https:\\\/\\\/mailrelay.com\\\/en\\\/#\\\/schema\\\/logo\\\/image\\\/\",\"url\":\"https:\\\/\\\/mailrelay.com\\\/wp-content\\\/uploads\\\/2019\\\/05\\\/mailrelay-logo.jpg\",\"contentUrl\":\"https:\\\/\\\/mailrelay.com\\\/wp-content\\\/uploads\\\/2019\\\/05\\\/mailrelay-logo.jpg\",\"width\":613,\"height\":291,\"caption\":\"Mailrelay\"},\"image\":{\"@id\":\"https:\\\/\\\/mailrelay.com\\\/en\\\/#\\\/schema\\\/logo\\\/image\\\/\"},\"sameAs\":[\"https:\\\/\\\/www.facebook.com\\\/Mailrelay\\\/\",\"https:\\\/\\\/x.com\\\/mailrelay\",\"https:\\\/\\\/www.youtube.com\\\/mailrelay-email-marketing\"]},{\"@type\":\"Person\",\"@id\":\"https:\\\/\\\/mailrelay.com\\\/en\\\/#\\\/schema\\\/person\\\/015806c54f5ded021ad304cd2e1b8c1d\",\"name\":\"No\u00e9 Soriano\",\"image\":{\"@type\":\"ImageObject\",\"inLanguage\":\"en-US\",\"@id\":\"https:\\\/\\\/secure.gravatar.com\\\/avatar\\\/3f16046acc14e3a26903ab4e9b4ba51e9b4b7b0c22b4f9f65f61bbfb98aed442?s=96&d=mm&r=g\",\"url\":\"https:\\\/\\\/secure.gravatar.com\\\/avatar\\\/3f16046acc14e3a26903ab4e9b4ba51e9b4b7b0c22b4f9f65f61bbfb98aed442?s=96&d=mm&r=g\",\"contentUrl\":\"https:\\\/\\\/secure.gravatar.com\\\/avatar\\\/3f16046acc14e3a26903ab4e9b4ba51e9b4b7b0c22b4f9f65f61bbfb98aed442?s=96&d=mm&r=g\",\"caption\":\"No\u00e9 Soriano\"},\"sameAs\":[\"http:\\\/\\\/mailrelay.com\"],\"url\":\"https:\\\/\\\/mailrelay.com\\\/en\\\/blog\\\/author\\\/noe-soriano\\\/\"}]}<\/script>\n<!-- \/ Yoast SEO plugin. -->","yoast_head_json":{"title":"Anti-Spam Systems: What They Are and How to Tell If You're Blacklisted","description":"Mailrelay explains what anti-spam systems are and the types that exist, such as Robinson lists, anti-spam systems and block detection. Only here!","robots":{"index":"index","follow":"follow","max-snippet":"max-snippet:-1","max-image-preview":"max-image-preview:large","max-video-preview":"max-video-preview:-1"},"canonical":"https:\/\/mailrelay.com\/en\/blog\/2017\/05\/23\/what-is-an-anti-spam-system-how-can-it-block-an-email\/","og_locale":"en_US","og_type":"article","og_title":"Anti-Spam Systems: What They Are and How to Tell If You're Blacklisted","og_description":"Mailrelay explains what anti-spam systems are and the types that exist, such as Robinson lists, anti-spam systems and block detection. Only here!","og_url":"https:\/\/mailrelay.com\/en\/blog\/2017\/05\/23\/what-is-an-anti-spam-system-how-can-it-block-an-email\/","og_site_name":"Mailrelay","article_publisher":"https:\/\/www.facebook.com\/Mailrelay\/","article_published_time":"2017-05-23T06:00:29+00:00","article_modified_time":"2026-10-15T16:36:57+00:00","og_image":[{"width":630,"height":340,"url":"https:\/\/mailrelay.com\/wp-content\/uploads\/2017\/04\/sistemas-antispam.jpg","type":"image\/jpeg"}],"author":"No\u00e9 Soriano","twitter_card":"summary_large_image","twitter_creator":"@mailrelay","twitter_site":"@mailrelay","twitter_misc":{"Written by":"No\u00e9 Soriano","Est. reading time":"9 minutes"},"schema":{"@context":"https:\/\/schema.org","@graph":[{"@type":"Article","@id":"https:\/\/mailrelay.com\/en\/blog\/2017\/05\/23\/what-is-an-anti-spam-system-how-can-it-block-an-email\/#article","isPartOf":{"@id":"https:\/\/mailrelay.com\/en\/blog\/2017\/05\/23\/what-is-an-anti-spam-system-how-can-it-block-an-email\/"},"author":{"name":"No\u00e9 Soriano","@id":"https:\/\/mailrelay.com\/en\/#\/schema\/person\/015806c54f5ded021ad304cd2e1b8c1d"},"headline":"What are anti-spam systems? How to tell if your IP is on a spam blacklist","datePublished":"2017-05-23T06:00:29+00:00","dateModified":"2026-10-15T16:36:57+00:00","mainEntityOfPage":{"@id":"https:\/\/mailrelay.com\/en\/blog\/2017\/05\/23\/what-is-an-anti-spam-system-how-can-it-block-an-email\/"},"wordCount":2025,"publisher":{"@id":"https:\/\/mailrelay.com\/en\/#organization"},"image":{"@id":"https:\/\/mailrelay.com\/en\/blog\/2017\/05\/23\/what-is-an-anti-spam-system-how-can-it-block-an-email\/#primaryimage"},"thumbnailUrl":"https:\/\/mailrelay.com\/wp-content\/uploads\/2017\/04\/sistemas-antispam.jpg","articleSection":["Deliverability and Technical Aspects","email marketing"],"inLanguage":"en-US"},{"@type":"WebPage","@id":"https:\/\/mailrelay.com\/en\/blog\/2017\/05\/23\/what-is-an-anti-spam-system-how-can-it-block-an-email\/","url":"https:\/\/mailrelay.com\/en\/blog\/2017\/05\/23\/what-is-an-anti-spam-system-how-can-it-block-an-email\/","name":"Anti-Spam Systems: What They Are and How to Tell If You're Blacklisted","isPartOf":{"@id":"https:\/\/mailrelay.com\/en\/#website"},"primaryImageOfPage":{"@id":"https:\/\/mailrelay.com\/en\/blog\/2017\/05\/23\/what-is-an-anti-spam-system-how-can-it-block-an-email\/#primaryimage"},"image":{"@id":"https:\/\/mailrelay.com\/en\/blog\/2017\/05\/23\/what-is-an-anti-spam-system-how-can-it-block-an-email\/#primaryimage"},"thumbnailUrl":"https:\/\/mailrelay.com\/wp-content\/uploads\/2017\/04\/sistemas-antispam.jpg","datePublished":"2017-05-23T06:00:29+00:00","dateModified":"2026-10-15T16:36:57+00:00","description":"Mailrelay explains what anti-spam systems are and the types that exist, such as Robinson lists, anti-spam systems and block detection. Only here!","breadcrumb":{"@id":"https:\/\/mailrelay.com\/en\/blog\/2017\/05\/23\/what-is-an-anti-spam-system-how-can-it-block-an-email\/#breadcrumb"},"inLanguage":"en-US","potentialAction":[{"@type":"ReadAction","target":["https:\/\/mailrelay.com\/en\/blog\/2017\/05\/23\/what-is-an-anti-spam-system-how-can-it-block-an-email\/"]}]},{"@type":"ImageObject","inLanguage":"en-US","@id":"https:\/\/mailrelay.com\/en\/blog\/2017\/05\/23\/what-is-an-anti-spam-system-how-can-it-block-an-email\/#primaryimage","url":"https:\/\/mailrelay.com\/wp-content\/uploads\/2017\/04\/sistemas-antispam.jpg","contentUrl":"https:\/\/mailrelay.com\/wp-content\/uploads\/2017\/04\/sistemas-antispam.jpg","width":630,"height":340},{"@type":"BreadcrumbList","@id":"https:\/\/mailrelay.com\/en\/blog\/2017\/05\/23\/what-is-an-anti-spam-system-how-can-it-block-an-email\/#breadcrumb","itemListElement":[{"@type":"ListItem","position":1,"name":"Home","item":"https:\/\/mailrelay.com\/en\/"},{"@type":"ListItem","position":2,"name":"What are anti-spam systems? How to tell if your IP is on a spam blacklist"}]},{"@type":"WebSite","@id":"https:\/\/mailrelay.com\/en\/#website","url":"https:\/\/mailrelay.com\/en\/","name":"Mailrelay","description":"Mailrelay.com - Email Marketing Software","publisher":{"@id":"https:\/\/mailrelay.com\/en\/#organization"},"potentialAction":[{"@type":"SearchAction","target":{"@type":"EntryPoint","urlTemplate":"https:\/\/mailrelay.com\/en\/?s={search_term_string}"},"query-input":{"@type":"PropertyValueSpecification","valueRequired":true,"valueName":"search_term_string"}}],"inLanguage":"en-US"},{"@type":"Organization","@id":"https:\/\/mailrelay.com\/en\/#organization","name":"Mailrelay","url":"https:\/\/mailrelay.com\/en\/","logo":{"@type":"ImageObject","inLanguage":"en-US","@id":"https:\/\/mailrelay.com\/en\/#\/schema\/logo\/image\/","url":"https:\/\/mailrelay.com\/wp-content\/uploads\/2019\/05\/mailrelay-logo.jpg","contentUrl":"https:\/\/mailrelay.com\/wp-content\/uploads\/2019\/05\/mailrelay-logo.jpg","width":613,"height":291,"caption":"Mailrelay"},"image":{"@id":"https:\/\/mailrelay.com\/en\/#\/schema\/logo\/image\/"},"sameAs":["https:\/\/www.facebook.com\/Mailrelay\/","https:\/\/x.com\/mailrelay","https:\/\/www.youtube.com\/mailrelay-email-marketing"]},{"@type":"Person","@id":"https:\/\/mailrelay.com\/en\/#\/schema\/person\/015806c54f5ded021ad304cd2e1b8c1d","name":"No\u00e9 Soriano","image":{"@type":"ImageObject","inLanguage":"en-US","@id":"https:\/\/secure.gravatar.com\/avatar\/3f16046acc14e3a26903ab4e9b4ba51e9b4b7b0c22b4f9f65f61bbfb98aed442?s=96&d=mm&r=g","url":"https:\/\/secure.gravatar.com\/avatar\/3f16046acc14e3a26903ab4e9b4ba51e9b4b7b0c22b4f9f65f61bbfb98aed442?s=96&d=mm&r=g","contentUrl":"https:\/\/secure.gravatar.com\/avatar\/3f16046acc14e3a26903ab4e9b4ba51e9b4b7b0c22b4f9f65f61bbfb98aed442?s=96&d=mm&r=g","caption":"No\u00e9 Soriano"},"sameAs":["http:\/\/mailrelay.com"],"url":"https:\/\/mailrelay.com\/en\/blog\/author\/noe-soriano\/"}]}},"uagb_featured_image_src":{"full":["https:\/\/mailrelay.com\/wp-content\/uploads\/2017\/04\/sistemas-antispam.jpg",630,340,false],"thumbnail":["https:\/\/mailrelay.com\/wp-content\/uploads\/2017\/04\/sistemas-antispam-150x150.jpg",150,150,true],"medium":["https:\/\/mailrelay.com\/wp-content\/uploads\/2017\/04\/sistemas-antispam-300x162.jpg",300,162,true],"medium_large":["https:\/\/mailrelay.com\/wp-content\/uploads\/2017\/04\/sistemas-antispam.jpg",630,340,false],"large":["https:\/\/mailrelay.com\/wp-content\/uploads\/2017\/04\/sistemas-antispam.jpg",630,340,false],"1536x1536":["https:\/\/mailrelay.com\/wp-content\/uploads\/2017\/04\/sistemas-antispam.jpg",630,340,false],"2048x2048":["https:\/\/mailrelay.com\/wp-content\/uploads\/2017\/04\/sistemas-antispam.jpg",630,340,false],"testimonials":["https:\/\/mailrelay.com\/wp-content\/uploads\/2017\/04\/sistemas-antispam-110x59.jpg",110,59,true],"author-image":["https:\/\/mailrelay.com\/wp-content\/uploads\/2017\/04\/sistemas-antispam.jpg",60,32,false],"mailrelay-email-template":["https:\/\/mailrelay.com\/wp-content\/uploads\/2017\/04\/sistemas-antispam.jpg",600,324,false]},"uagb_author_info":{"display_name":"No\u00e9 Soriano","author_link":"https:\/\/mailrelay.com\/en\/blog\/author\/noe-soriano\/"},"uagb_comment_info":2404,"uagb_excerpt":"In this post we want to go over which anti-spam systems and other checks are taken into account when deciding whether an email send is spam and can cause our newsletters to be blocked.","_links":{"self":[{"href":"https:\/\/mailrelay.com\/en\/wp-json\/wp\/v2\/posts\/34196","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/mailrelay.com\/en\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/mailrelay.com\/en\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/mailrelay.com\/en\/wp-json\/wp\/v2\/users\/7"}],"replies":[{"embeddable":true,"href":"https:\/\/mailrelay.com\/en\/wp-json\/wp\/v2\/comments?post=34196"}],"version-history":[{"count":14,"href":"https:\/\/mailrelay.com\/en\/wp-json\/wp\/v2\/posts\/34196\/revisions"}],"predecessor-version":[{"id":105658,"href":"https:\/\/mailrelay.com\/en\/wp-json\/wp\/v2\/posts\/34196\/revisions\/105658"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/mailrelay.com\/en\/wp-json\/wp\/v2\/media\/15594"}],"wp:attachment":[{"href":"https:\/\/mailrelay.com\/en\/wp-json\/wp\/v2\/media?parent=34196"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/mailrelay.com\/en\/wp-json\/wp\/v2\/categories?post=34196"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/mailrelay.com\/en\/wp-json\/wp\/v2\/tags?post=34196"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}