As designed, when performing the action Dismiss on threat events, there’s an internal limitation of 50 characters for the user's email address length. So, if the email address for the affected user has more than 50 characters, the Dismiss action can’t be performed.
For example:
- Email address with 51 characters, just above the design limit: my-email-is-longer-than-50-characters@mycompany.com
- Email address with 49 characters, just below the design limit: the-email-has-forty-nine-characters@mycompany.com
