[NTLUG:Discuss] user replication between 2 linux servers

[Steve Jackson]

This may be a remedial question (or not), but if I want to put 2 linux
servers on the net as redundant mail servers (SMTP and POP3), is there an
automated way to replicate user changes between the 2 machines?  I could
probably write a set of scripts to accomplish this, but I thought I'd ask
ya'lls opinions/advice first.  Are there any commercial products to do this?
Is there built-in functionality to do this?  Having one box take over duties
for the other, in case of failure, is no prob, but making sure the users on
box1 and box2 are the same (with the same password) is my sticky point.