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Mail: Can't send messages, "Cannot send message using the server smtp.xxxxx.com" alert appears
After deleting and recreating an account in Mail, you might not be able to send emails even if you can receive them. When you try to send a message, this alert may appear:
"Cannot send message using the server smtp.xxxxx.com"
This happens if the Simple Mail Transport Protocol (SMTP) server, used for outgoing messages, was incorrectly entered with the first account even if it was correctly entered for the replacement account.
Solution
You should first verify that the network connection you're using is the correct one for the ISP that you want mail to communicate with.
1. Open Mail.
2. From the Mail menu, choose Preferences
3. Click Accounts.
4. On the Outgoing Mail Server (SMTP) pop-up menu, choose Edit Server List.
5. Delete all entries for the SMTP server that is mentioned in the error, and click Done.
6. Configure the current SMTP server by clicking Server Setting.
Note: If you need to use multiple SMTP servers for multiple Mail accounts, see this document.
7. Send a test message to your email address.
Ska testa och se om det fungerar eller inte.