Cannot send email - SMTP fails diagnostics

Noticed many people having this problem going back as far as 3 or 4 year. Alas all solution I have read have not resolved the issue for me - I have tried all policy settings and all ports; 25, 465 and 587  and SMTP server still it fails and won’t be fixed.  Oddly 3 days ago , I sent an email without a problem, so I know it can do it sometimes!  Using em Client version 7.0.27943.0, Windows 10 also tried turning off virus protection but that did not help either. 

Hello Juliet,

Please provide logs so we can see what is causing this issue.
To copy logs go to Menu>Tools>Operations>Log and copy with Ctrl+A, paste to notepad, then send the file to cooper@emclient.com.

So among my many other problems, this one has surfaced today as well.

Trying the diagnostics and fix from the account settings does not help.

I have Thunderbird running with the same account details and setting, and there is no problem.

Disabled all firewall and AV software - no result.