YouTrack Not Sending Emails

I have the following products installed.

• Hub (2020.1)
• Upsource (2020.1.1802)
• YouTrack (2020.4.6808)

I have configured Hub and YouTrack to have Notifications enabled. Both are configured with the same connection information, user, and password. When performing a "send test" function in both, the Hub email states it sends and I receive such; the YouTrack email states it is successful but I never receive the emails. The email credentials are correct as they have been tested in Hub and an independent utility. 

Where can I look to find out more details about the notifications? I need to get my YouTrack notifications working (again). Please note, the notifications were working without issue for a long time, and then suddenly they have stopped sending. I have tested sending to multiple email addresses from my work to Gmail and other personal accounts.