Many of you have asked us why emails sent to some online email providers sometimes seem to arrive late.
Outlook/Hotmail and other ISPs limit the number of messages a given IP can send within a period of time, based on the IP’s reputation. When an IP exceeds its sending limit, every SMTP command will receive error code 421.
That is why emails with the status “Queued” sometimes appear in the detailed sending reports. This means that when the email is sent, the destination ISP returns an error code and the system will try to deliver it later.
These retries can go on for up to 72 hours, so an email may occasionally reach its recipient several hours late. This isn’t due to any issue at Mailrelay, but because the destination server hasn’t accepted it until then.
The million-dollar question is: how many emails can you send in a bulk email campaign before messages start being rejected and queued? Unfortunately, there’s no answer to that question. The destination ISP adjusts this figure based on the reputation of the sending IPs and domain, spam complaints, spam traps, opens, and so on.
What is important to point out is that by following the sending rules they require, you are very unlikely to see any queuing or rejections at all.
What can you do if you have queued emails because you’ve exceeded the sending volume per IP?
First, contact our Customer Support team so we can look into the problem with you personally. There can be several reasons why this problem is happening, so it’s best to look at each case individually and draw up an action plan.
In general, you should check whether you’re getting spam complaints, make sure your databases are 100% confirmed with double opt-in, check that your designs follow the recommended guidelines, and confirm that SPF and DKIM are set up correctly, among other things. This post has a summary of the main points to check.
If, after checking all these points and confirming that you meet them, the destination ISP keeps rejecting your emails, you can contact them and ask them to review your case, although it’s important to note that the answer isn’t always positive.
This type of rejection is usually related to your overall reputation, your IP warming and sending volume ramp-up, and, more generally, your email marketing deliverability.