Found a bug in the Copy to Postfix option in the Manage SSL Certificate area.
My main.cf prior to clicking: smtpd_tls_mandatory_ciphers = medium
After clicking: smtpd_tls_mandatory_ciphers = medium, high
I was unable to send via SMTP after this and received the following errors:
Jun 18 05:44:53 mars postfix/smtpd: warning: c-24-16-194-164.hsd1.wa.comcast.net[188.8.131.52]: invalid TLS cipher grade: "medium, high": aborting TLS session
This is some info I found: https://bugs.launchpad.net/ubuntu/+source/dovecot/+bug/365390
The fix is to keep either medium or high as the value and restart postfix.