Email notifications in Applications Manager may stop functioning in Applications Manager version 9.3.1 or below.
Restarting Applications Manager fixes the issue
bug in Applications Manager that is fixed in Applications Manager 9.3.2.
Release : 9.2.x, 9.3.0, 9.3.1
Restart Applications Manager processes or service (Windows)
Upgrade to fixed version Applications Manager 9.3.2
Bugfix information found here and noted below:
SMTP connections not timing out due to bad connection (AM-1481)
A problem has been fixed where SMTP connections (notifications) were not timing out. The connection timeout for notifications has been set to 30 seconds with a read/write timeout of 3 minutes.