I looked on the two main sites you should look when you need this kind of information: Google and Microsoft.

Here’s what these have to say:

Configuring POP3 For WM 6:

In this case you have to follow 3 easy steps:

Set up Gmail as a POP3 account

Automatically forward Gmail

Access Gmail from the Internet

Source: Microsoft.com Support

Configuring IMAP For WM 6:

Enable IMAP in your Gmail settings.

Open the Start menu and select Programs > Messaging > New E-mail Account.

Enter your Gmail username (including ‘@gmail.com’) in the E-mail Address field.

Uncheck the box to get settings automatically from the Internet and select Next.

Select Internet e-mail as your email provider in the drop-down menu.

Enter your name as you want it to appear in sent emails.

Enter a descriptive name for the email account and select Next.

Enter ‘imap.gmail.com’ in the Incoming Mail Server field.

Select IMAP4 as the Account type from the drop-down menu and select Next.

Enter your Gmail username (including ‘@gmail.com’) and password.

Select Next.

Enter ’smtp.gmail.com’ in the Outgoing (SMTP) Mail Server field.

Make sure that the Outgoing server requires authentication box is checked.

Select the Advanced Server Settings link.

Make sure that the Require SSL box is checked for both incoming and outgoing emails.

Select The Internet as the network connection from the drop-down menu.

Select Done and then Next.

Select how often you want your phone to send/receive emails from the drop-down menu.

For more download options, select the Review all download settings link.

Select Finish.

Check our recommended client settings, and adjust your client’s settings as needed.

Source: Gmail support

From what I’ve read here for example, POP3 is better then IMAP, having some advantages (like security), but I thought some of you might need IMAP for some reason.