Mailbox unavailable. The server response was: 5.7.1 …
Mar 22, 2017 · That means that you have to use an existing mail account at the SMTP server (your client domain mail id), connect to the server using an authentication method, and send the password for your account. You are probably already using authentication with your mail clients (Outlook, Thunderbird, etc). Just use the same parameters as there.
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