Roaming

Hello,one and all ...
I have this sendmail installation that restricts the access to the 
POP server with the help of the "access" file.

However, now and then I need to connect to the server from outside
my network and the assigned IP address is unknown at the time.
This makes POP3/SMTP access impossible from outside the network.
Can any one help in suggesting a solution for this? I.E. I need 
access
to the e-mail system from outside the network yet I need
to preserve the security of the system

Any help will be greatly appreciated.
Alex