553 5.7.1 <user@example.com>: Sender address rejected: not owned by user
You logged in as one user but sent as another address
Seen in Postfix (reject_sender_login_mismatch)
Postfix checks that the authenticated user is allowed to use the MAIL FROM address, and this login doesn't own that address.
Common causes
- The mail client logs in with one account but sends from another address or alias.
- The address is missing from smtpd_sender_login_maps.
- An app uses a shared SMTP login but sets each user's own From address.
How to fix it
- Send from the address that belongs to the account you log in with.
- On the server, add the address or alias for that login to smtpd_sender_login_maps and reload Postfix.
- Use a separate login per sending address where possible.
Got a different message? Paste it into the error explainer.
Related errors
- 550 5.4.1 Recipient address rejected: Access denied · Microsoft 365 rejected an unknown recipient at the edge
- 550 5.7.708 Service unavailable. Access denied, traffic not accepted from this IP · Microsoft 365 blocked the tenant's outbound mail
- 530 5.7.57 Client not authenticated to send anonymous mail during MAIL FROM · The app sent to smtp.office365.com without logging in
- 535 5.7.139 Authentication unsuccessful, SmtpClientAuthentication is disabled for the Tenant · Microsoft 365 refused the SMTP AUTH login
- 550 5.7.520 Access denied, Your organization does not allow external forwarding · Automatic forwarding to an outside address is blocked
- 550 5.1.8 Access denied, bad outbound sender · The sending account was blocked for spam
- 451 4.7.500 Access denied, please try again later · Microsoft 365 is temporarily throttling the sending IP
- 552 5.2.2 The recipient's inbox is out of storage space · The recipient's mailbox is full
- 552 5.3.4 Your message exceeded Google's message size limits · The message is larger than the server accepts
- 535 5.7.8 Username and Password not accepted · The SMTP login was rejected
- 450 4.2.0 <user@example.com>: Recipient address rejected: Greylisted · The message was greylisted; it will be accepted on retry
- 530 5.7.0 Must issue a STARTTLS command first · The server requires TLS before it accepts mail