Simplenews + Mime Mail + SMTP = occasional blank email I have a client site that uses the Simplenews module with the Mime Mail and SMTP Authentication modules. The subscriber list has a little over 300 email addresses, and when newsletters go out the cron sends out batches of 100 messages per hour. Things usually go off without a hitch, but with the last newsletter one of the batches sent contained blank messages. I have been unable to reproduce the problem. Someone else reported the same problem here:

https://www.drupal.org/node/2378147

. . . but has of yet there has been no response, and I'm not convinced the problem lies with the Simplenews module itself. Has anyone else seen anything like this problem?
First step. Have you combed your logs in Drupal for errors?  And have your also looked at your web server PHP error logs?

With this random problem you are having I would expect to see something going on in the logs.

I have never used the Simplenews module or reviewed it's code so I cannot say how well the authors of the module addressed error handling the module.

Clearly you have a problem and it's been reported by other people. If you find no error in the logs then I would say that potentially the module does not have enough error handling written into it to diagnose the problem.

For what it's worth (purely for your own information), I will say that attempting to do an email newsletter from a a web server is not the preferred method. An email service provider should be used for that functionality if you have any concern for deliver-ability of your newsletter.