There are too many kinds of phones. I cannot see your phones. You must do it yourself.
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No matter which phone, the principle is the same
you must change BOTH “Incoming Mail Server” and “Outgoing Mail Server”
Find the “Incoming Mail Server”, change it to h12.hksx.com
Find the “Outgoing Mail Server”, change it to h12.hksx.com
Try to send yourself an email. If you can receive it, it is done.