Whois Mail Server information. Need to access email account.

Hello there.  We recently have had an employee leave one of our other buildings.  Now we need to access this former employee's Outlook account and set-up a forwarding rule, among other things.

The problem lies in the fact that I cannot find out here email supplier.  The email address is listed under a new company that only does broadband.  So I cannot find out who is actually supplying the email address.

The new company is saying it is not them.  The only information I have to go on is the mail server address.

This is;

mail.digitelonline.co.uk

Now I have tried to find digitelonline, or digitel online through google, but cannot locate them.

Is there a whois search that will allow me to see who's responsible for this mail server, then I can try and get in contact with them.

Thanks.