Antispam filters<br>

Antispam filters or spam filters are applications used to prevent spam from reaching email inboxes.
They are not infallible, but they prevent users from seeing their inboxes flooded with spam.

The way users behave when they receive emails helps filters to learn and improve their performance, and this, together with the constant updating of RBLs (black lists of spammers), makes the criteria for classifying emails as spam more and more precise.

On the other hand, each company can add its own rules to its antispam filter so that, locally, the accuracy of spam detection is improved.

What can be done to overcome spam filters?

There are no magic formulas for overcoming antispam filters, what you can do is to follow these tips so that the antispam filters have a better perception of any email they receive from your domain:

• At DNS level. You must have the DNS correctly configured, at least the SPF record, DKIM and DMARC.
  Also leave your domain registration data visible in WHOIS queries.
  
• Don’t use purchased databases. Always use double opt-in lists or, if not possible, opt-in lists to prevent email recipients from flagging you as spam, since spam reports cause antispam filters to block new emails from the same domain.
  
• Take care of the subject line and content.
  Don’t write all the text in capital letters and avoid the use of suspicious words or phrases, like: free, gift for you, opportunity, etc.
  This would increase the chances of your email being blocked by antispam filters.
  
• Send with a quality infrastructure.
  Sending a single email or an email marketing campaign are very different things, so rely on a quality email marketing platform such as Mailrelay.
  
• Avoid sending attachments. If you receive an email with an attachment, the anti-spam filter should analyze not only the subject line and content, but also the attachment, which increases the chances of being flagged as spam.
  
• Include option so that users can unsubscribe.
  If you create email marketing campaigns, always add an unsubscribe link in your emails so that users can request removal; this will decrease the number of spam complaints.
  
• Don’t use URL shorteners or paste URLs directly.
  Using URL shorteners will trigger the spam filters, because the system will detect that you are trying to hide the original URL.
  On the other hand, don’t paste URLs directly in the text, try to use text links and you will avoid being penalized.
  
• Segment and send.
  A properly worked database is very valuable, so segment it and update it frequently.
  You also have to avoid spamtraps and delete hard bounces.
  
• A design with images and text.
  Never create a newsletter using only an image; you should add texts and links as well.
  Also avoid embedding text in images, as this is often interpreted as an attempt to hide the text from spam filters.
  

How to fool spam filters?

If you have in mind to deceive the antispam filters it is fair to indicate that it is highly improbable that you will be able to do it, it is not that it is impossible because in some occasion your antispam system has let pass spam messages to your inbox, but it is not within the reach of everybody.

If you overcome the filter, it will be counterproductive for your next mass mailings; once you are detected, the filters will block your next campaigns and this will affect your marketing strategy for a long time.