Students and Staff both have access to email via Exchange.
All accounts are scanned (in and out) using Policy Patrol from Red Hat Software which deals with Keywords, Spam, attatchments, custom rules etc.
Neither staff or students can access any other mail service (we use RM SafetyNet Plus and have the web based mail filter switched on).
The view is that
1) We can't control or restrict content from an external email source, and as it might be inappropriate or virused it is prohibited and
2) As all have school-based email, there should be no requirement to access personal mail
(in terms of staff access this causes the occasional comment/query now and again, but when you point out that the use of the Internet connection is for teaching and learning purposes only, and that personal addresses should not be used for work etc, the discussion doesn't carry on much longer!)