Wrong contact avatar displayed when email addresses differ only by dot-separated prefix

Steps to reproduce

1. Create two contacts in the Contacts app:
   Contact A: name@domain.com (with or without avatar)
   Contact B: firstname.name@domain.com (with avatar)

2. Send an email from name@domain.com.

3. Open the "Sent" folder.

4. Check which avatar is displayed for the sent email.

Expected behavior

The correct contact avatar should always be displayed based on an exact email address match.
If no avatar is assigned to the email address in the Contacts app, only the automatically generated initials avatar (e.g., first letters of first and last name) should be shown.

Actual behavior

The avatar of a different contact is displayed when the email addresses differ only by a dot-separated prefix.

Apparently, the matching is not based on an exact email address comparison.

Mail app version

5.6.11

Nextcloud version

31.0.13

Mailserver or service

Postfix 3.10.5/Dovecot 2.4.1

Operating system

Debian 13.3 (64-bit)

PHP engine version

PHP 8.3

Nextcloud memory caching

'memcache.local' => '\OC\Memcache\APCu', 'memcache.distributed' => '\OC\Memcache\Redis'

Web server

Apache (supported)

Database

MariaDB

Additional info

No response