If you use the stock email client from Android 4.x, then be VERY careful if you are using POP3 download. It appears that the stock client will download all the messages from your mail server every time it checks for mail, so you could use a lot of data.

(eg - see http://android.stackexchange.com/questions/22086/ics-stock-email-client-consumes-too-much-traffic-for-pop3-accounts )

We recommend using IMAP4 (requires VPOP3 Enterprise), which supports proper synchronisation, or use an alternative email client app.