Froxlor is open source server administration software. Prior to version 2.3.6, in `EmailSender::add()`, the domain ownership validation for full email sender aliases uses the wrong array index when splitting the email address, passing the local part instead of the domain to `validateLocalDomainOwnership()`. This causes the ownership check to always pass for non-existent "domains," allowing any authenticated customer to add sender aliases for email addresses on domains belonging to other customers. Postfix's `sender_login_maps` then authorizes the attacker to send emails as those addresses. Version 2.3.6 fixes the issue.