If you can’t send your emails from MS Outlook, the problem is very likely (but not exclusively) related to your SMTP server – the server taking care of the whole email delivery process. That is why it’s always better to rely on a professional server.
Read more here:- https://www.datarecovo.com/unable-to-send-emails-from-ms-outlook/
Check your internet connection. Yup.
Check your SMTP server details. This is an extremely common mistake: you have set up your mail client with the wrong SMTP parameters. ...
Verify all usernames and passwords. ...
Check your SMTP server connection. ...
Change your SMTP port. ...
Control your antivirus or firewall settings.
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