Any word on this? It appears to be a smartermail issue.

 

Outlook 2013, Outlook 2016, And EMClient all have the same issue with sending attachments >20MB. Suspect phone mail clients are also effected, I just haven't been able to find a client that allows me to attach more then 20MB worth of attachments.

 

I've ensured that attachment sizes are all high. And can send via SMTP and webmail with no issue. 

Hello.  Outlook 2013/2016 have their own built-in maximum attachment size of 20Mb.  If you wish to increase that limit, you would need to add a registry entry per this Microsoft KB Article.  I hope this helps.