the issue is that Tomcat does not have privileges to bind the 25 port. We configure the Tomcat server to use the "tomcat" user and not the root user for security reasons.
A possible workaround is to configure the Alfresco email server in a different port, for example 2025.
Then, as email servers use the 25 port, create a port forwarding rule in your system to redirect all requests from 25 port to 2025 port. It is only necessary to run the following command:
sudo iptables -t nat -A PREROUTING -i eth0 -p tcp --dport 25 -j REDIRECT --to-port 2025
You can check the iptables rules with this command:
sudo iptables -t nat -L -n -v
Check that you added port 25 in your firewall to have external access. Restart the alfresco application, this could take some time:
sudo installdir/ctlscript.sh restart tomcat
From another machine you can check that everything is ok using telnet:
telnet your_host_name 25
You can see something similar to this:
Connected to your_host_name .
Escape character is '^]'.
220 alfresco.com ESMTP SubEthaSMTP 3.1.6
I hope it helps,
Edit: Added entry to Alfresco wiki http://wiki.bitnami.com/Applications/Bitnami_Alfresco#Inbound_email_configuration