An e-mail error 554 is sometimes considered a panacea for e-mail errors. It is typically used in case of generic delivery failure for which another e-mail error code does not directly define a problem. Some mail servers also use a 554 error even though there is already a specific error code. The server should receive a feedback message with a variant of the email error 554 in the subject and the body of the message should contain the original message that you attempted to transmit.
A healthy mail system should be able to deliver mail within 20 hops. However, this limit may be exhausted when: Mail is stuck in a send loop – We found that incorrectly configured MX mail or sender gateways forwarded messages to the sender, resulting in a loop. Intermediate servers add too many headers – Anti-spam servers or gateway clusters can inject too many headers that will be interpreted as an email loop.
Let’s take a look at these points in more detail.
Mail loop within Sender’s MX or Gateway
All messaging systems depend on destination “pointers” that indicate where the destination mailbox is located. These pointers include DNS records, mail user databases, host entries, and so on. In a perfectly functioning system, these pointers perfectly route the mail to the destination server. But all this can break during a redesign of the messaging system and direct the mail elsewhere or to the sending server itself.
We’ve seen such situations during:
DNS & Mail routing errors after hosting account transfers
When a website is transferred to a new server, its DNS MX records and SMTP routing data must be modified. We have seen instances where these changes did not occur either because of software errors or because of custom settings that were broken during the migration. This leads to an exchange of mail between the old and the new server.
Mail config errors after server migrations
During server upgrades or infrastructure migrations, it may be necessary to reconfigure the mail servers with new IP addresses and routing tables. We found problems with incorrect configuration of the routing tables, which caused the mail to remain connected to the sending server, creating a loop.
Gateway or anti-spam server installation/upgrades
Some companies have set up a separate anti-spam server or mail gateway to improve mail filtering. But if the DNS settings and outgoing mail routes are not configured correctly, the messages will be sent back between the sender’s MX and the gateway.
To resolve these issues, we enable debugging and track the error to the exact parameter that caused the failure.