höw-to configure N900 for Gmail , google mobile IMAP settings and configuration

http://mail.google.com/support/bin/answer.py?hl=en&answer=78799

You can use the following information to configure IMAP with many mail clients. If you encounter difficulties, we suggest contacting your mail client's customer support department for further instructions -- we're unable to provide assistance with configuring mail clients not listed here. Incoming Mail (IMAP) Server - requires SSL: imap.gmail.com
Use SSL: Yes
Port: 993
Outgoing Mail (SMTP) Server - requires TLS: smtp.gmail.com (use authentication)
Use Authentication: Yes
Use STARTTLS: Yes (some clients call this SSL)
Port: 465 or 587
Account Name: your full email address (including @gmail.com) Google Apps users, please enter username@your_domain.com
Email Address: your full Gmail email address (username@gmail.com) Google Apps users, please enter username@your_domain.com
Password: your Gmail password


Please note that if your client does not support SMTP authentication, you won't be able to send mail through your client using your Gmail address.

Also, if you're having trouble sending mail but you've confirmed that encyrption is active for SMTP in your mail client, try to configure your SMTP server on a different port: 465 or 587.