I posted an article on how to access your Gmail account using SnapperMail via Gmail's POP3 feature. Read on to see what other PalmOS email application works as well...
I tried several other email applications, and found another PalmOS email applocation that works very well with Gmail's SSL-secured POP3 connection: Mark/Space Mail from Mark/Space. Like SnapperMail, it is a very slick, full-featured email client, and it provides SSL connectivity. (For those that don't know, this is a "Secure Sockets Layer" security model that Gmail (and many othe Web sites) uses to create a secure connection. This should help boost user confidence in Gmail's security policies.)
To configure Gmail, just enable POP3 in your Gmail Account by clicking on "Settings", click on the "Forwarding and POP3" tab, and then make the appropriate settings based on your situation.
Next, launch Mark/Space Mail, and select "Options > Accounts" and tap "New". Fill in page one with your account information. Tap the Page 2 icon and fill in your username with your FULL Gmail email address. Next, enter "pop.gmail.com" into the "POP3 Host" field and assign your password. Enter "smtp.gmail.com" into the "SMTP Host" field. Next, tap the Page 3 icon and check off BOTH "Use SSL" boxes. For the POP3 port, use "995" and for the SMTP port, use "465" or "587". Check off the "Allow SMTP Authentication" checkbox and then enter your full Gmail email address in the "SMTP Username" field and assign the password.
Tap "OK", tap "Done", and when you tap "Send/Receive", you should connect properly.
This works like a charm on my PalmOne Tungsten C.