I was working through a strange issue where emails were bouncing with varying issues like syntax, relay etc. But it felt random. What it came down to is that all mailings via cron (cv api job.execute) were failing whereas those via the web interface for schedule jobs (Execute Now) were working.
The point above was only in hindsight. I thought my mailing solution (Office 365) was not playing well, but also happened with sendgrid which made me think it was something local.
One post I stumbled on made me look at the difference of web server PHP vs cli based php, and sure enough the apache php.ini had mcrypt.so extension but not the cli!
I hope this may help others. I was stumbling upon a lot of suggestions to have Net_SMTP not verify peer but I did not think that was correct solution.
As for a resolution, maybe a check or something that puts a warning in the log when cron runs?