We host our email on an internal server. Recently we have started getting bouce backs from various other servers. Most seem to have the following error:

Reason: Remote SMTP Server Returned: 550 Sender IP reverse lookup rejected

I have checked all the blacklists and we don't seem to be listed on any. I have done a reverse lookup from several sites and they all seem to be responding with the correct rDNS of the mailserver.

Does anyone have any suggestions?

Thank you!

  • Some mailservers don't like reverse lookups that give a hostname that look like dynamic IP addresses, e.g. dialup- – wurtel May 2 at 14:22
  • Obviously something changed if it "suddenly" happens (but it doesn't have to have happened on your side). If some DNS records were changed, it takes some time to replicate it to every nameserver, so it could be a faulty DNS record. It could also be some wrong NAT rule that someone configured, etc. What TLD is your domain? I assume you checked with this tool, too: mxtoolbox.com/diagnostic.aspx ? – Lenniey May 2 at 14:35
  • We use the default format mail.mydomain.de. So our TLD is .de – joize May 2 at 14:50
  • It "suddendly" happens since wen are located in the US-Market too. So the problem mostly appears on recipients in the US. The mails are sent as user@mydomain.com from the mailserver mail.mydomain.de – joize May 2 at 14:52
  • Well, mydomain.com and mydomain.de are not the same... – Lenniey May 2 at 14:56

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