503 This mail server requires authentication

503 This mail server requires authentication when attempting to send to a non-local e-mail address. Please check your mail client settings or contact your administrator to verify that the domain or address is defin ed for this server.

In Outlook Click on Tools>Email Accounts>Change/Edit>More Settings check the box "My outgoing server (SMTP) requires authentication


Related:

I can receive emails but I cannot send

Please try one of the following:

• Contact your ISP and request port 25 to be opened
• Change SMTP address to your ISP's, example smtp.att.net
  

Outlook for your domain name
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