What common email errors mean (mailbox full, 550, relay not permitted, authentication failed) and what to do about each one.
Read the bounce first
When an email can't be delivered, the sender gets a bounce (a "Mail delivery failed" or "Undelivered Mail Returned to Sender" message). It contains a three-digit code and a short reason:
- Codes starting with 4 (for example 421 or 451) are temporary. The sending server tries again on its own for a while.
- Codes starting with 5 (for example 550, 552 or 554) are permanent. The message was rejected and won't be retried. Fix the cause and send it again.
The text after the code tells you who rejected the mail and why. To see what happened to a message on our side, use Track Delivery in cPanel.
Errors when you send from your mail app
"535 Incorrect authentication data"
The username or password for the outgoing server is wrong. The username is the full email address and the password is the mailbox password. Check it in webmail (see Log in to webmail) and type it again in the app's outgoing server settings.
"SMTP AUTH is required for message submission on port 465"
The app tried to send without logging in. Turn on authentication for the outgoing server ("My outgoing server requires authentication" or similar) and use the same login as for incoming mail.
"… is not permitted to relay through this server without authentication"
This is the "relay denied" error. Our server only sends mail to other domains for users who log in. The full text starts with "Please turn on SMTP Authentication in your mail client." Turn on authentication as above, and use your server name with port 465 (SSL/TLS) or 587 (STARTTLS) as outgoing server, not port 25. The settings are in Email server settings and ports.
"Sender verify failed"
The server could not confirm that the sender address can receive mail, for example because the sending domain has no working mail setup. If it's your own domain, check its MX record (see Add or change MX records). If a website form sends with a made-up "From" address, change the form to use a real address on your domain.
Connection or timeout errors
The app can't reach the server at all. Some networks block outgoing mail ports: switch the outgoing server between port 465 (SSL/TLS) and 587 (STARTTLS), and check the server name.
Bounces about the recipient
"Mailbox full", "quota exceeded" or "over quota"
The receiving mailbox has no space left. If it's one of your mailboxes, free up space or give it more (see Free up mailbox space with Email Disk Usage and Change the storage space of a mailbox). Mail rejected while the box was full doesn't come back by itself: ask the sender to send it again. If it's someone else's mailbox, let them know another way.
"550 … user unknown", "No such user" or "No such person at this address."
The address doesn't exist. Check the spelling. "No such person at this address." is the text our server sends back for unknown addresses on your domain when its Default Address is set to bounce them (see Set a default address (catch-all)). If the address should exist, create it (see Create an email account).
"The mail server could not deliver mail to … The account or domain may not exist, they may be blacklisted, or missing the proper dns entries."
This is how Track Delivery describes a failed delivery. Check the recipient address and domain for typos. If the address is right, read the bounce or the View Details window in Track Delivery for the receiving server's own reason.
Rejected as spam, "blocked" or "policy" errors (often 550 or 554 with 5.7.x)
The receiving server didn't trust the message. Set up SPF, DKIM and DMARC for your domain (see Fix email going to spam: SPF, DKIM and DMARC) and avoid sending bulk mail from a normal mailbox. If the bounce names our server's IP address on a block list, open a ticket and include the full bounce.
When to contact us
Open a ticket if the same error keeps coming back after the steps above. Include the full bounce message (copy all of it, including the technical part at the bottom), the sender and recipient addresses and the time you sent the mail. That lets us find the message in the server logs quickly.
Related articles
- Check where an email went with Track Delivery in cPanel
- Email server settings and ports (IMAP, POP3, SMTP)
- Free up mailbox space with Email Disk Usage in cPanel
- Fix email going to spam: SPF, DKIM and DMARC
Still stuck? Open a support ticket and we'll help.
