Unable to Send Email
Please confirm your SMTP settings and try again.

Log is in unifi-core/http.log or unifi-core/notifications.log

error: /notifications/testEmail request failed: Server terminates connection. response=421-4.7.0 Try again later, closing connection. (EHLO)
421-4.7.0  For more information, go to
421 4.7.0  https://support.google.com/a/answer/3221692 2adb3069b0e04-5990da6159dsm300782e87.46 - gsmtp: 421-4.7.0 Try again later, closing connection. (EHLO)
421-4.7.0  For more information, go to
421 4.7.0  https://support.google.com/a/answer/3221692 2adb3069b0e04-5990da6159dsm300782e87.46 - gsmtp
error: https 295ms 503 POST /notifications/testEmail
info: https 178ms 200 PATCH /api/system
error: /notifications/testEmail request failed: 1010D7B67F000000:error:0A00010B:SSL routines:ssl3_get_record:wrong version number:../deps/openssl/openssl/ssl/record/ssl3_record.c:
354:
error: https 280ms 503 POST /notifications/testEmail

Cleanup and repair MongoDB. MongoDB is stored on HDD (slow).

UniFi - Repairing Database Issues on the UniFi Network Application