gateway security

Hi I would like to make our mail server/masquerading gateway more secure while still being able to log in remotely (using ssh I presume?) for admin purposes. It is also running Webmin. What is the best way to do this? The internet connection is only a dial-up ISDN, but the gateway can be connected for several hours at a time, and I am concerned about possible attacks. It's running SuSE 6.3. Thanks Grant. Grant R Walton New Creation Family Church PO Box 1638 Cresta South Africa 2118 Tel. +27-11-792-1151 --- Outgoing mail is certified Virus Free. Checked by AVG anti-virus system (http://www.grisoft.com). Version: 6.0.230 / Virus Database: 111 - Release Date: 01/01/25