When your provider declines a message, it gives BlueMail a reason, and BlueMail passes that reason straight to you instead of failing quietly. Your message is moved to Drafts so it is never lost, and the notice names both the account and the code:
[your account] was unable to send an email. The message was moved to Drafts folder. Error: 535
An SMTP error code is your provider's own explanation of why the message could not go out, which makes it the quickest way to know what to put right. The most common cause is simply an account that needs to re-authenticate, and updating your password clears it. Others are temporary conditions on your provider's server that resolve on their own.
Below is a list of common error codes and the reasons they occur.
Common Error Codes
- 421 – Service not available. The connection will be closed.
- 432 – A password transition is needed. This error is often related to an authentication issue.
- 447 – Your message timed out because the receiving server was busy. Try resending your message after some time.
- 450 – Command failed because the user’s mailbox is unavailable (e.g., locked). Try again later.
- 451 – Command aborted due to a server error. Not your fault.
- 452 – Command aborted due to insufficient system storage on the server.
- 454 – Authentication failed. You must authenticate before sending mail (try to update your password within BlueMail).
- 501 – Syntax error in command arguments.
- 503 – Bad sequence of commands encountered by the server.
- 504 – Command parameter not implemented.
- 511 – Bad email address. Check the recipient's email address for typos.
- 521 – Connection rejected. This domain doesn't accept mail or the server might be down.
- 523 – Size limit exceeded. Your email is too large to be processed by the recipient's server.
- 530 – Authentication required. Authenticate your email account before sending mail (try to update your password within BlueMail).
- 535 – Authentication failed. Authenticate your email account before sending mail (try to update your password within BlueMail).
- 550 – User’s mailbox is unavailable (e.g., not found, or rejected for policy reasons).
- 551 – Recipient not local to the server. The server gives a forwarding address to try.
- 552 – Action aborted due to exceeded storage allocation.
- 553 – Command aborted because the mailbox name is invalid.
- 554 – Rejection from the recipient domain. This means 'Not allowed'. The address in the "Sent From" or "Send To" headers appears to have insufficient submission rights, is invalid, or is not authorized with the authentication used. Please check the recipient address.
Messages You May See Instead of a Code
Some conditions come through as plain wording rather than a number:
- No valid authentication mechanism found. Please check your SMTP settings and re-add the account. Your outgoing server settings need a look, and re-adding the account is the fastest way to rebuild them correctly.
- Too many simultaneous connections for account [your account] (SMTP). Try again in 15 minutes. Your provider is limiting how many connections one account may hold at once. Waiting the quarter hour clears it.
Whatever the wording, your message is waiting in Drafts. See What happens if my connection drops while sending an email? for how BlueMail keeps it safe.
