550 5.7.1 — Message blocked (Proton Mail)
PermanentReputation
Retrying will not help. The message will not be delivered.
The reply
550 5.7.1 Message blocked.Proton refused the message and gives almost no detail. In practice the two things worth checking first are whether your IP is on a public blocklist and whether the message authenticates — Proton weighs both more than the large receivers do.
What it means
A permanent policy rejection. Proton does not run a postmaster dashboard or a feedback loop, so there is no view into their assessment of you. That makes the externally checkable things — blocklists, SPF, DKIM, DMARC, reverse DNS — the whole of the available diagnosis.
Why it happens
- The sending IP is listed on Spamhaus or another public blocklist.
- SPF, DKIM or DMARC missing, failing or unaligned.
- No reverse DNS on the sending IP, or a PTR that does not match the HELO name.
- A new IP with no history, in a range known for abuse.
- Content resembling bulk or promotional mail.
What to do
- Check the sending IP against Spamhaus ZEN, Barracuda and SpamCop, and request delisting where listed.
- Verify SPF, DKIM and DMARC all pass and align with the From: domain.
- Confirm forward-confirmed reverse DNS on every sending IP.
- Send a plain-text message to see whether the content is implicated.
- If everything checks out and it persists, contact Proton support with the exact reply and your sending IP.
Questions
Is there a postmaster contact?
No dashboard and no feedback loop. General support is the only route, so have your authentication and blocklist status demonstrably clean before you write.