Can an external domain be used for an alias?
Knowledge Base > FAQ's > Can an external domain be used for an alias?
By Mads Petersen on October 6, 2021

Kolab Now supports the use of multiple aliases and identities, however we do not allow external aliases from domains that are not linked to our servers, or domains that are not under our users’ control (e.g., or

This is not a technical limitation as much as it is a security feature. Kolab Now has a strict SMTP access policy that defines who is allowed to send mail, and under what identity, and to which recipients.

We focus on security and privacy, which implies that the recipient of any mail sent through our systems can clearly and without ambiguity identify the sender at any time. With external aliases, this currently cannot be guaranteed. At this time we do not see a method to reliably verify the ownership of an external domain.

Users can change the “Reply To” value on an email, but not the “From” value. See how to configure the identities in the article about  creation of an alias.