RFC compliant mail address not allowed
CiviCRM has some kind of format check when entering emails.
However, in certain cases it is not possible to enter email addresses, although they rfc compliant.
When an email address with a "-" at the end (as firstname.lastname@example.org ) is entered in a profile or in the contact summary, an error message occurs, the contact cannot be saved.
It should be possible to enter an email address like: email@example.com
CiviCRM 5.28.2 and CiviCRM 5.24.5
I believe that worked better previously, because we have a few cases like that within our database!