Use of X509v3 Subject Alternative Name

[Jorey Bump]

I'm curious about the use of X509v3 Subject Alternative Name in
certificates, and if they pose any problems when used in production.

For example, if I obtain a certificate with the Common Name of
www.example.com for primary use over HTTP, and add an X509v3 Subject
Alternative Name of mail.example.com for dual use over SMTP (server) and
 HTTP (for webmail), will there be issues? Is support widespread enough
to safely implement this approach (assuming I can get a commercial cert
issued)?