Tested it quickly
We might add it, but once enabled you must use the samba AD field userPrincipalName or the mail ldap field to login, it means user@FirstDomain.com
The issue for me is that a user who uses to send email with the user@AliasDomain.com will want probably to use it and he will have an Authentification error. I understand it is a nethserver limitation
I have no clue how the proposed will impact my situation … I will have to test. I will also have to re-read this later today and make sure I get what you are changing and why 
Hello @stephdl, sorry for my late reply for this topic - I had some days off. My input on that:
Also field MailFieldName is an issue:
My installtions all have to deal with mutliple email domains. To make sogo working well I need to set MailFieldName correct (this is mandatory fo meeting invitations to work!!). I need to be able to set this field as needed (different Domains!).
A) nethserver = Samba DC:
MailFieldNames = (“E-Mail”);
or commetn this filed out (which results into same).
// MailFieldNames = (“userPrincipalName”);
Now I can set my individual E-Mails in field ‘E-Mail’ using Windows AD Tools:
This solution works fine, but can not be done in Nethserver only (besie using phpLDAPadmin).
B) nethserver = stand alone:
MailFieldNames = (“l”);
Now I do not have a separate field for email and I had to use one of the existing fields to enter my correct email. I ended up to use existign field ‘l’ (done via phpLDAPadmin). I used an existing one to avoid possible problems with future updates, hoping that this solution will last for long:
This is more a dirty hack but working.
I would like to sees a possibility to enter ‘sogo email’ inside nethserver user setup. This field should be used for Sogo MailFieldNames then.