Hello. I'm having this problem for a long time ago. But as I had this problem only on one computer and not on the other one that I have been using for administration, I didn't care much about this problem. But now I have the same problem on both computers.

I go to webmail login page and if I login with user@domain.com or user, I only can see the administration page for domain.com. I have the same user as administrator on most of my domains.

This is the url I'm send after login: webmail/interface/root#/settings/domain/domain-general-settings (for domain.com)

I checked my history and saw this url for system admin:
webmail/interface/root#/sysadmin/manage

So, I go to login, put only user (not user@domain.com), I'm redirected to webmail/interface/root#/settings/domain/domain-general-settings and then I change url on the browser and try to go there: webmail/interface/root#/sysadmin/manage
And I get an error message: "User does not have rights to perform this action". Or sometimes I get a blank page.

So, my question is: Please, ¿How can I login as a system administrator? 

Thank you!