webmail and domain alias not working

[tusm]

After a migration from other plesk server the virtual subdomain "webmail" didn't work under domain alias, working ok on parent domain.

I mean

mydomain.com have hosting set up and myalias.com is alias of that hosting.

myalias.com --> mydomain.com

webmail.mydomain.com works ok.
webmail.myalias.com shows default server page.

It's like serveralias directive not working in apache config.


Thanks
Regards