Fastmail · permanent error
551 5.7.1: not authorised to send from this address
Fastmail refused to send your message because you are not set up to send from the address in its From header. Verify the address first.
- Fastmail
- Provider
- Permanent (5xx)
- Class
- Sources checked
- Author
At a glance
- Code
- 551 5.7.1
- Provider
- Fastmail
- Temporary or permanent
- PermanentRefused for good: the message comes back to the sender, and resending it gets the same answer.
- Who has to act
- The sender. The fix is on the sending side: your domain, your server or your list.
- What the server says
551 5.7.1 Not authorised to send from this header address
What it means
Fastmail lets you send from your own addresses and from external ones, but only after the address is set up and verified for sending. This 551 5.7.1 means the address in the From header of your message is not authorised for your account. Go to Settings, then My email addresses, and find the address you used. If it shows an Unverified status, you need to set up authenticated sending before Fastmail will send from it.
Common causes
- The From address is an external address that was added but never verified.
- The From address is not set up in your Fastmail account at all.
- A mail program or app is set to send with a different From address.
How to fix it
- 01Open Settings, then My email addresses, and find the address you sent from.
- 02If it is Unverified, set up authenticated sending for it.
- 03Or change the From address in your mail program to one of your Fastmail addresses, and send again.
Sources
What this page rests on, checked on 20 Oct 2026. The explanation is ours; the reply text is the server's.
- Why messages bounce back (Fastmail help center)fastmail.help
Related codes
- 535 5.7.8Authentication failed for an external address.Fastmail could not sign in to the outgoing server of an external address you send from, most often because its stored password has changed.
- 551User not local.The server does not deliver mail for this recipient and may suggest another address to try. The message was not accepted.
- 5.7.1Delivery not authorised.The receiving server refuses the message because this sender is not allowed to send to this recipient, as a result of filtering by host or by recipient.
5.7.1 at other providers
- 550 5.7.1Blocked by a domain policy.A rule set by the recipient's or the sender's Google Workspace admin blocks this message, so Gmail rejected it under that policy.
- 550 5.7.1Relay IP does not match the sending domain.Google's SMTP relay knows your IP, but the mail's sending domain is not one that IP is registered to relay for in your Workspace account.
- 550 5.7.1Blocked as likely spam.Gmail's filters judged this message likely to be spam and rejected it outright, instead of delivering it to the spam folder.
- 550 5.7.1IPv6 sender without PTR or authentication.Gmail rejected mail that arrived over IPv6 because the sending address lacks a matching PTR record, or the message failed authentication.
- 550 5.7.1Blocked for low IP reputation.Gmail permanently rejected the message because the IP it came from has a very low reputation with Gmail.
- 550 5.7.1Blocked for low domain reputation.Gmail permanently rejected the message because the domain it comes from has a very low reputation with Gmail.
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