Apple Mail error: Cannot send message using the server

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You may see an error message in Apple Mail that says:

Cannot send message using the server [server address]
The sender address [your email address] was rejected by the server [server address]

Or you just may not be able to send mail, without seeing an error message. In either case, there is something wrong with your outgoing server settings. Try these steps to resolve the issue.

  1. If you have the option on the error message, click Edit SMTP Server List.

Note: If you don’t have the error open, or don’t see this option: Select your account under Inbox, click the cog under the mailbox list, and select Edit “[your email address]”… Then click the menu next to Outgoing Mail Server (SMTP), and select Edit SMTP Server List…

2. Select the server in use by your account.
3. If you have multiple servers with the same name, you will need to remove the duplicates. Select the duplicate server, then click — below the list.
4. Click Advanced.
5. Make sure all the fields match your correct settings:

FieldShould be…
Automatically detect and maintain account settingsSelected
PortA port number from your Email Setup Center
Use SSLIf the port is listed in black, leave this unselected. If the port is listed in orange, make sure this is selected.
AuthenticationPassword
Allow insecure authenticationUnselected
User NameYour full email address
PasswordYour correct email password

6. Click OK.
7. If you are returned to the error message, select the server you just edited, and click Try With Selected Server.

More info