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This is a copy of a forum post from over a year ago. I have had this issue twice before and with enough pressure on Cox support they managed to fix their broken system. Come on Cox, do your job and fix this problem once again! FYI I am on port 465.
If I am on a Cox wifi outgoing mail works. Same on 4G. But if I am on a wifi other than Cox mail fails to send.
Here is a re-post of this same issue from days gone by.
For some reason, my phone won't send email - and it seems to be because it can't verify the SMTP server. My username and password are correct and I'm using SSL with port 587. I've turned the phone off and on, reset network settings, double-checked wifi and LTE settings and I even tried deleting the account and setting it up from scratch - despite all that, it will receive email but won't send. Thoughts?