Some ISP's are now restricting outgoing e-mail through third-party e-mail accounts. You can check their policies and see if they have a preferred method for sending outgoing e-mail.
Many ISPs allow you to send only through their system to prevent people for using their e-mail servers for spamming.
If you're receiving error messages from your e-mail client such as Outlook and Thunderbird, "error: could not connect to your outgoing SMTP server" chances are your ISP is blocking port 25. Port 25 is a common outgoing port for e-mail.
Possible solution: By changing your outgoing port from 25 to port 26, this could allow you to bypass your ISP mail servers.
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