Webmail url and SSL

[Tickit]

Hello,

I bought a SSL certificate for a domain "www.mydomain.com" and I have a big problem because I want to use horde... and when I type webmail.mydomain.com I have (logical) a certificate error.... then I like to use horde by this way : www.mydomain.com/webmail... How can I do this ?

Thank you in advance for you answer.