Need to change the hostname name of server

I need to change the hostname of one of my servers runnin Debian Lenny and ISPconfig3.

Is it safe to do this on a server that has already some websites and email's on it?
Do I only need to run:

Code:

 
/etc/init.d/hostname.sh stop
echo new.servername.tld > /etc/hostname
/etc/init.d/hostname.sh start

and set the new hostname in the /etc/hosts file?

Or do I need to change more things?
Setting the reverse DNS will be done by mij ISP.

 

It's a singleserver setup.
What about Postfix and Courier? Do I need to change anything in here?

 

For Postfix, see Till's post. For Courier, there shouldn't be anything to change.