I've installed the Squirrelmail package and I can't log in. I've tried using firstname.lastname@example.org and domain.com_user (I've changed web[ID] for [DOMAIN] so I can login with user@domain format string), neither work.
This wont work. ISPConfig does not allow usernames with @ inside. It is not enough to replace the webID with the domain placeholder. Please use the username and not the email address for logins.