Well I found a not too recent web posting on the web where the poster was having same problem with a Samsung. Apparently the outgoing port should be 25. Mine has always been set to 587 as per TT info. That has cured the problem, but for some reason when I go to settings it has reverted to 587 so has to be reset. No way to save the setting. Will go back to the Android forum and check.
How to get Windows 10 now: how to download and install Windows 10 even if GWX.exe is missing