Are you actually in theatre? Where are you trying to connect from/to?
If you are on a UK military base, the internet connection is provided by Paradigm and you shouldn't have any problems accessing the usual webmail services.
If you are trying to connect to Afghan civvi internet, it can be a bit dodgy sometimes, with connections dropping out. In Kabul the link is generally a wireless one from wherever you are to a satellite repeater station which then connects to the internet via Germany.