Mail stays in the delivery queue or gets bounced back


What to do if the email get bounced back?


If the mail-server is configured correctly and has no known issues (like a full disk, cpu overload), but still email does not arrive and is instead waiting in the delivery queue or bounced back to the sender then the cause is usually one of the following;

  • The issue is on mail-server: Unfortunately it happens very often that people are not aware of problems happening on their mail-server. Double-check this with your systems manager.
  • The mail-server is filtering the emails deliver by the spam-filter: This will make the mail-server blacklists or misjudging the headers that Spamexperts added.

If you use Spamexperts platform, make sure that the final receiving mail-server does not have spam-filtering turned on, to avoid the chance of blocking the spam-cluster itself. If it is really necessary to turn on spam-filtering, even though the emails are been filtered already, please make sure the following IP's are whitelisted in your firewall:

IPv4 IPv6 2a00:f10:10a:e::25:587:2 2a00:f10:10a:e::25:587:5

2a00:f10:10a:e::25:587:10 2a00:f10:121:400:42c:78ff:fe00:42e/64  

If the server is not filtering the emails coming from the Spamexperts platform, please contact our support team sending a email to

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