For a [gmail] incoming port server, you can either choose IMAP (port 993) or POP (port 995) protocol - summarized here.
From gmail help article, it seems IMAP is a more modern protocol, so I chose it.
For Incoming Mail Server, assuming you chose the IMAP protocol instead of POP:
Navigate to Settings/Configuration/General Settings/Configure the incoming email gateway
Name : *anything you want*
Server Type : IMAP server
Server Name : imap.gmail.com
Port : 993
SSL/TLS : [â] *make sure to check this or else you will get an error*
Supply your email address and password.
I did not supply any other information to the Server Action Field or to the Advanced tab.
Only OpenERP users that supply their email address and password to the Configuration can fetch the unread messages in their inbox and will appear in the Messaging Module.
As I have read, OpenERP will fetch every 5 minutes but you can press Fetch Now to force the fetch.
BTW, i'm using google apps email server but I'm using a custom domain, so my email looks like: firstname.lastname@example.org but is still served by gmail
actual screenshot of my settings
For an outgoing email setup, even if I configure all the emails of many users, the email is always sent from the first configured [outgoing] email, also asked here
All emails that arrive on my inbox is from email@example.com. I also don't know how to change the "from" address. Maybe Fabien's suggestion of configuring a local server will make it work.