I need to change my Surgemail domain name from ehowe.com to mail.ehowe.com

Currently email client's use ehowe.com as the server hostname for IMAP, 
POP and SMTP.
I need them to change that to mail.ehowe.com.
When I change my server hostname field in my email client to 
mail.ehowe.com it doesn't work. I'm guessing because the SSL certificate 
is for ehowe.com.

Currently I have:
domain_name = ehowe.com
url_host = ehowe.com

My DNS entries are
A record is mail.ehowe.com
MX record is mail.ehowe.com

I'm not sure what to change for DNS or Surgemail and I'm afraid of 
messing the server up. I do know I will have to redo the SSL certificate 
though.

I appreciate any insight so I don't screw my server up.

Thanks,
Randy