If you find that you are able to receive email but cannot send email, your email client may not be properly configured for SMTP authentication, which is required by your mail server.

SMTP authentication means that a username and password are required for outgoing mail connections as well as for incoming connections.

In the Outgoing server section of your mail client, you will want to ensure that both the full email username (user@yourdomain.com) and the email account’s password are entered, and that either the Server Requires Authentication box is checked (if present), or that the Authentication type selection is not set to None.

If you’re using a mail client such as Mac Mail and you have multiple email accounts on your server configured in the mail client, you will want to ensure that each account has its own outgoing server configured with its corresponding email account password; you will not be able to use the same outgoing server with multiple email accounts due to the SMTP authentication requirement.