Guest email address does not allow subaddressing

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Steps to reproduce

1. invite guest from file sharing using email address with sub addressing <name>+<postfix>@domain.tld thows error cf. actual behaviour
2. invite guest from admin user -> add account using email address with sub addressing <name>+<postfix>@domain.tld works OK. But after refresh I see this account is not added to guests group. Login does not work.
3. Adding a normal user account from admin user -> add account using email address with sub addressing <name>+<postfix>@domain.tld works OK. This user can login but is obviously NOT added to Guests user group.

Expected behaviour

Consistent behaviour and support of email address with sub addressing <name>+<postfix>@domain.tld in all NC apps. Support of RFC +@domain.tld email addresses (also known as "plus addressing" or "subaddressing") is addressed in RFC 5233, titled "Sieve Email Filtering: Subaddress Extension". It is known as a very helpful extension e.g. during testing.

Actual behaviour

Tell us what happens instead, if possible also add a screenshot

Server configuration

Hosted Nexcloud instance - no access to CLI

Nextcloud version: (see Nextcloud admin page)
Nextcloud Hub 10 (31.0.8)

Browser

not dependence on Web Browser expected

The issue names no files, tests, or entry points. Reproduce the file-sharing invitation and admin account flows with a plus-addressed email, then trace their handling and guest-group assignment; done means consistent support for these addresses across the described Nextcloud guest flows and successful guest login.