I do but it co-relates to the Alternative UPN Suffixes i think.

Maybe we can look into automating those (add/remove) for SolidCP

but i am not sure if it then requires the AD DNS settings for that domain aswell.

A solution about that is fixing the UPN on the OU level

In order to that open Active Directory Users and Computers, (make sure on View that "Advanced Features" is checked

Browse to the OU the client is residing, right click it -> Properties -> Attribute Editor -> edit uPNSuffixes field to contain the UPN(s) of the customer

It is a feature SolidCP should be probably implement to be done automatically

@mourikis I understand thats the way to apply Additional domain suffix's, however in the past we seen just adding any domain in there causes AD related errors (missing AD DNS Records which for example your main AD Domain would have in AD DNS).

To properly implement this we have to fully understand the rammifications of adding in additional domains to AD Suffix and make sure AD Does not try to ultilize this as an actual AD Domain (as for all intents and purpouses 99,99% for SolidCP Exchange domains will be external only).