Sending email from AP9361 via IONOS fails (error 554, transaction failed)

[colinbutcher]

This error occurs with both firmware v7.1.2 and v7.1.8.

Sending email via IONOS fails. Sending email via a different mail provider (Blueyonder, now VM) works, but when forwarded to an IONOS email account, the forwarded email is rejected by IONOS mail servers with the same 554 transaction failed error.

The AP9631 seems to be sending email with a header that does not pass the IONOS checks, hence the rejection by the IONOS mail servers. 

Here's the information that IONOS provide:

554 Transaction failed, reject due to policy restrictions

Problem:

The email was rejected by the IONOS SMTP server because the standards defined in RFC 5321 and RFC 5322 were not adhered to.

Solution:

The email client must meet the following criteria:

• The header lines of the email must contain exactly one valid "Date" line according to RFC 2822.
• The following header lines may only exist once: From, Sender, To, CC, Subject
• The header lines mentioned must be syntactically correct

Note: The To and CC lines can contain multiple recipients.

In accordance with the recommendations from RFC7103, incorrect messages are not automatically corrected by IONOS, otherwise DKIM signatures become invalid. For more information about DKIM signatures, see the IONOS article Configuring DMARC Records for a Domain.

[Teken]

What NMC firmware version worked before you upgraded?!?

[colinbutcher]

V7.1.2 (released in Spring 2023) used to work, until Fall 2023 or thereabouts.

I believe that IONOS, as with other mail providers, have tightened up their checking fairly recently.

The recent release of V7.1.8 (Fall 2024) prompted me to check if it would now work, which it does not.

I think that the firmware needs to be modified to correctly format the mail headers in accordance with standards as currently applied.