Apache James is a very nice e-mail server to be used in a development or test environment, where you need to integrate with an email system. I mentioned it in an earlier post. It supports smtp, pop, nntp (news) and imap.
It's installation is as simple as can be: just unzip the tool, set your JAVA_HOME environment variable and run the appropriate run.sh or run.bat script (given your OS being either Unix/Linux or Windows). The only thing you need besides the zip is a Java Runtime Environment that is at least of version 1.4.2.

For most systems this is all you have to do to get it running. But I found that on IBM AIX (5.x) it is a little less obvious. Getting it running is not an issue, but as soon as you want to add a user, you'll run into the error:

Exception: Security error: java.security.NoSuchAlgorithmException: SHA MessageDigest not available

And after that the telnet connection is closed.
It turns out that the security-provider packages are not registered properly. To get it right there are two things to do.

1. Make sure that the JAVA_HOME is pointing to the jre folder in the root folder of the java-installment on your system. So like: /usr/java5_64/jre instead of /usr/java5_64. Also make sure that there is a lib/ext folder (/usr/java5_64/jre/lib/ext) that contains a <make>jceprovider.jar, eg. sunjce_provider.jar or ibmjceprovider.jar.
   
2. Change <james-home>/bin/phoenix.sh to register the extensions:

• Find the line:
  

JVM_EXT_DIRS="$PHOENIX_HOME/lib:$PHOENIX_HOME/tools/lib"

• Change it to:

JVM_EXT_DIRS="$PHOENIX_HOME/lib:$JAVA_HOME/lib/ext:$PHOENIX_HOME/tools/lib"

Now james can be started using the run.sh/run.bat scripts and using the telnet console you should be able to succesfully add users.

It might be that on your system, the system administrators block port 25(smtp) and 110 (pop). That would prevent james to startup the smtp and pop services.
In the <james-home>/apps/james/SAR-INF/ there is a config.xml file. In that file you can find a line:

<pop3server enabled="true">

There you can choose to disable pop by changing the enabled attribute. But benaath that line there is a port element. You could change that instead to for example 8110. That would enable pop-support on the 8110 port. You should instruct your client to use that port off course.
The same counts for smtp-support. That can be found at:

<smtpserver enabled="true">

For smtp you could choose to set the port to 8025.