Email Queue - Not using SMTP configuration after upgrade

[bdm]

I recently upgraded to FusionPBX 5.1.1 from 5.X (I can't remember the exact release). Everything appeared to be working great until I learned voicemail and faxes were no longer arriving via email. After looking into the issue, I found that my SMTP server defined in the default settings is not being used. All messages are hitting the local systems MTA (EXIM4) and sitting in its queue. When conducting email tests, they are processed via my SMTP settings and delivered properly. This issues seems similar to that discussed on this thread: https://www.pbxforums.com/threads/voicemails-are-not-getting-emailed.6524/ However, none of these solutions worked for me.

Any thoughts on how to resolve this?

Thanks in advance!