Using PHP connecting to an POP/IMAP server is a relatively easy process, it can be useful for using webmail or to allow a script to download all emails and store in a database for instance.
The function required to make the connection is imap_open, it expects three parameters first the connection string made up of the remote host and mailbox folder, followed by the username and password.
a typical example:
imap_open("{imap.gmail.com:993/ssl/novalidate-cert}INBOX","user@gmail.com","passwordofuser") or die(imap_errors());
The above should work just fine, I've found a large number of blogs/articles using that path.
I've not had any success with that, Google may have updated this recently, tested the above locally and on a remote server.
In order to make the connection remove the novalidate-cert.
imap_open("{imap.gmail.com:993/ssl}INBOX","user@gmail.com","passwordofuser") or die(imap_errors());