It's really easy, once you put together all the proper settings--which are miserably hard to find.
Why Lion defaults to IMAP, I am not sure--my iDevices still work fine on the same accounts, and they are all, of course, IMAP. I just did not want to manage my mail that way--and the choice should have been made obvious, I'm looking at you, Apple.
1. It worked better for me to set up Mail, Contacts and Calendars in System Preferences after setting up accounts in Mail.
2. Open Mail Preferences under the Mail menu, and add your email account by hitting the + sign.
3. BUT, after you fill in the fields, HOLD DOWN THE OPTION KEY before you hit Create--and it will change into CONTINUE.
4. In the next screen that will appear, pull down the menu that says IMAP, where you will see POP just above that. Select POP.
5. Give the account any Description you choose--this is what you will see in the Mail list of mailboxes.
6. Change Incoming Mail Server from what is already filled in--imap.gmail.com--to pop.gmail.com.
7. Tricky one: in Gmail, always fill in your entire email address wherever it asks for Username.
8. Then, of course, password.
9. In next screen: check Use SSL, authentication Password
10. Next screen: In Description, again give the account the same nickname as before.
Outgoing mail: smtp.gmail.com
Do not check use only this server unless you've a reason to.
Check Use Authentiation, again filling in your entire Gmail address as Username. And your pasword.
11. Next screen will be Account Summary, where you can check your settings--to some degree, can be changed in Mail Preferences, but do click Take Account Online, and see what happens.
12. If you can't connect, it's okay, we aren't finished with Gmail's fussy requirements.
13. Go back into Mail Preferences--and here's another Gmail gotcha: Under the Accounts panel, you want everything filled out as prior instructions as to username.
Under Mailbox Behaviors, Gmail POP can handle whatever you input. I like to delete Junk and Trash when quitting mail, moving Trash to the Trash Mailbox.
The third panel, Advanced: Enable This Acount, of course, and Include when checking. Remove a copy works fine for me unchecked, but for purposes of setup, previous Mail versions have wanted this checked (I unchecked it later) so try one or the other, but don't hit Remove Now. Leave the Prompt empty.
BIG gotcha: Gmail wants the port set to 995 (not 993). Again, SSL and password.
14. Now let's go back to the first panel, Account Information, where you will find a pulldown menu under Outgoing Mail Server (SMTP.)
Go ahead and pull down and select Edit SMTP Server List ...
15. Now when that window opens, you will see two panes: under Account Information, the server name is smtp.gmail.com, the Description--there I filled in my whole Gmail addy, not sure why--and under Advanced: Use default ports, Use SSL, Authentication: password, Username: whole Gmail address ... and fill in your password.
With the warning that Mail frequently loses this, so when you can't connect, you will come back here and see if it's gone missing again--probably a keychain issue.
Closing Mail Preferences will ask you to Save these changes. You should be good to go!
And if you're not? Run Connection Doctor, under the Window Menus, and click right on whatever shows as not connecting--which will take you to the place in Mail Accounts that needs it's settings fixed. And when you do imput them correctly, Connection Doctor immediately tries to connect again, it's very handy.
Keychain Access will ask you for your password, if it needs to.
Hope this works for you ... and that anyone more expert will add notes as neeeded.
POP mail works just fine in Lion. If that's what you prefer, go for it!