I tried using the suggestion earlier but it didn't work. However after several hours of messing with POP setting in the Mail app, this is what worked for me.

1) Under incoming server User name, I did NOT use @gmail.com after my gmail account name

2) For the outgoing server username, I USED @gmail.com after my gmail account name

After that, I don't know why, but it sends and receives like it should. This might be some freak occurrence with my computer but, I hope it helps other people too! =)

FOX!!! Sorry guys. Ignore what I just posted. It worked that way that one time that I tried it will those setting. Well, I have two gmail accounts on my MAIL program, but one works the other doesn't. I pretty much copied the setting of the working account to the broken account, with the exception of account name. I don't get what going on. Anyone have any ideas on why it doesn't work?