Thank you Igor. My current hosting company doesn't provide subdomains, so I can't see what happens when I go to webmail.mydomain.com.
When I go to webmail.mydomain.com do I see the Plesk login page, or the Roundcube login page?
Is it a problem (as in a security issue) that webmail uses http instead of https?
(And can i just buy and install a ssl certificate for webmail subdomain, or will that not work?)