Best ways to secure POP/SMTP on server?

[andreas palsson <did@algonet.se>]

Hello.

I have a server connected to the internet, and I wonder how I can secure
my box in a good way.

I have plans to set up POP3 and SMTP for my users to connect and use the
services  from anywhere they may be.

But I also realize that by doing that, my system could be misused by
other people than my users.

I am most worried about SMTP, in which there seems to be no(?) actual
password-verification.

Does anyone have encountered a similar situation?
Suggestions on what to do? What to read?

Regards...
	Andreas