On my OnePlus 3 mobile using GMAIL I an having issues sending mail from my NTLWORLD account. When I try and confirm my SMTP settings it says host can not be reached. I do not have this issue on my Samsung tablet or any other device or email client. I have checked the correct settings. I have also carried out several malware scans and everything is normal.
This tricky to diagnose if the phone is not relaying the full error code that the VM server is sending out. The port and ssl settings look correct and have got authentication switched on. Can you check that the From address you have entered for the account exactly matches the email address you are using to authenticate the smtp server.
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