Your client needs to support HTTPS and HTTP Basic Authentication. The feed URI is:
https://gmail.google.com/gmail/feed/atom
Sample:
<feed version="0.3">
<title>Gmail - Inbox for
danny.ayers@gmail.com</title>
<tagline>New messages in your Gmail Inbox</tagline>
<link rel="alternate" href="http://gmail.google.com/gmail"
type="text/html"/>
<modified>2004-10-14T21:50:53Z</modified>
<entry>
<title>Reconnect with former colleagues</title>
<summary>
Dear Danny, With over one million professionals
registered on LinkedIn, chances are good you will …
</summary>
<link rel="alternate" href="http://gmail.google.com/gmail"
type="text/html"/>
<modified>2004-10-09T07:33:00Z</modified>
<issued>2004-10-09T07:33:00Z</issued>
<id>tag:gmail.google.com,2004:1150609973351906273</id>
<author>
<name>LinkedIn Updates</name>
<email>updates@linkedin.com</email>
</author>
</entry>
...more entries...
</feed>
I wonder if they're going to support posting too?
[Danny]