Email should not be longer then 50 characters, otherwise an error message shows up.
Release : 12.3 Component : AUTOMATION ENGINE
This is by design as per documentation of USR Table
As per documentation of AE 21.0
The AE 12.3 documentation is about to be updated with this information.
Workaround consisting in respecting this limitation and provide emails that do no exceed 50 letters.
Product Management is aware of this issue, and is thinking about changing. These should be introduced in an near, but still unknown Version.