Unfortunately Google is increasingly making it harder to use gmail with a native mail client. They don’t use normal means of authentication so your client has to have built-in Google support. They’re introducing new types of emails that can only be opened from a web browser or Google’s proprietary email client. I won’t be surprised if I wake up one morning to see that gmail simply doesn’t work with normal mail clients anymore.

I think Google requires that you perform a web login every now and then to keep the account active. IIRC They don't count POP/IMAP auths as logins.