In Acrobat Pro DC, when adding a new Digital ID, there is an attribute 'Email'. Please allow all email addresses in that field. Do not arbitrarily limit characters in email addresses to: a-z A-Z 0-9 . @ - _

Today I want to use an address, from+dsig@example.com, using a '+' character. This is perfectly legal in my email address, and I should be able to use it in a digital ID.

Beyond that, email addresses are no longer limited to a subset of ASCII Latin letters. Addresses in many scripts are now legal, e.g. Hindi ईमेल-परीक्षण@सार्वभौमिक-स्वीकृति-परीक्षण.संगठन or Arabic
تجربة-بريد-الكتروني@تجربة-القبول-الشامل.موريتانيا or Chinese 電子郵件測試@普遍適用測試.組識.澳門 or many others.

How to reproduce:
In Acrobat Pro DC (2021.001.20135) on macOS 10.13.6 High Sierra, do Acrobat Pro DC… Preferences…. Signatures… Identities and Trusted Certificates, More… The Digital ID and Trusted Certificates Settings dialogue appears.
Click on the "Add Digital ID" icon (picture of an ID card with a "+" on top). The "Add Digital ID" dialogue appears.
Select radio button "A new digital ID I want to create now", and press Next >. The Add Digital ID dialogue becomes a form with 7 fields.
In the "Email Address" field, type an address containing a "+", or a non-Latin character. Fill in the other fields reasonably. Press Next >.

Observed behaviour: The following alert dialogue appears:

Acrobat Security
The 'Email' attribute contains an illegal character.
Only the following characters are permitted: a-z A-Z 0-9 . @ - _

Expected behaviour: the Digital ID creation process continues, accepting the email address.

Discussion: Digital IDs are stored in files with the extension .p12.
They are presumably PKCS #12 format archives. RFC 8399 "Internationalization Updates to RFC 5280" specifies how to store such international email addresses, and my own little address with a "+" sign, in digital IDs.
I have a Digital ID in a .p12 file, which was created by a previous version of Adobe Acrobat Pro in December 2020, which has "+" sign in the email address. Thus Acrobat's limitation on email address characters seems to be a recent regression.