The phpbb_validate_email function returns the language key EMAIL_INVALID when an email address does not match the email regexp, but the name of this key in the language pack is actually EMAIL_INVALID_EMAIL.

Similarly, when the email_check_mx configuration option is enabled and phpbb_validate_email cannot find a valid MX record, it returns the language key DOMAIN_NO_MX_RECORD, but the language key in the language pack is actually DOMAIN_NO_MX_RECORD_EMAIL. Also, this key is in the ucp.php language file which is not loaded by memberlist.php?mode=contactadmin so does not work with that form.