Thunderbird IMAP push email
Using Thunderbird as the e-mail client of your choice and the IMAP protocol to fetch and manage your mail?
RFC 2177 defines IDLE, an extension to the IMAP protocol allowing mail clients to change into an idle mode while keeping the TCP-connection open. This allows the servers to notify the clients of new mails on arrival (the so-called push e-mail).
Not all e-mail providers support IMAP IDLE, though – you should check whether your mail provider supports it by opening a telnet connection to the IMAP server (standard port for IMAP is 143) and sending 001 capability. If the answer contains „IDLE” your server supports IMAP IDLE.
GMail for example answers
* CAPABILITY IMAP4rev1 UNSELECT IDLE NAMESPACE QUOTA XLIST CHILDREN XYZZY
001 OK Thats all she wrote!
There's one thing to look out for, though – Thunderbird only sends the IDLE command (effectively enabling push e-mail) if you disable the „check for new mail every nth minute”-option. I could not find any documentation on that feature – however using Help » Mozilla Thunderbird Help causes a 404 File Not Found error for me anyway (using the German version of Thunderbird).
Steve Jobs would say: „Exchange for the rest of us” – using GMail, IMAP and Thunderbird.