Enhanced SMTP status code · RFC 3463 · IANA
5.7.30 REQUIRETLS support required
The message arrived with a REQUIRETLS requirement (RFC 8689), and none of the servers it had to go to next support it.
- Class: Permanent failure
Class 5: a permanent failure. Resending the same message will not help: something about the message, the sender or the destination must change (RFC 3463 §3.1).
Also seen as:
4.7.30 - Subject: X.7 · Security and policy
Policies (per-host or per-recipient filters) and cryptographic operations; up to the sender, the recipient or both.
- Associated basic codes (IANA registry)
How 5.7.30 appears at providers
The exact text from the provider's documentation, as you see it in the bounce, and what it means.
Gmail
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550 5.7.30
This message was blocked because it didn't pass DKIM authentication. Gmail requires bulk email senders to authenticate their email with DKIM.
The message does not pass DKIM, which Gmail requires from bulk senders. Check with DKIM generator.
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421 4.7.30
Your email has been rate limited because DKIM authentication didn't pass for this message. Gmail requires all email bulk senders to authenticate their email with DKIM. Authentication results: DKIM = Did not pass.
The message does not pass DKIM, which Gmail requires from bulk senders. Check with DKIM generator.
What you can check here
Have the whole error message?
Sources: RFC 5321 · RFC 3463 · RFC 3464 · IANA · Gmail · Microsoft 365 · read on 26 September 2026