If you are trying to send a mail from a process in LiveCycle ES, you may encounter the following exception in the log:
java.lang.RuntimeException: javax.mail.MessagingException: Could not connect to SMTP host: <hostname>, port: 25; nested exception is: java.net.SocketException: Software caused connection abort: connect
If you are using Virus Scanner software they often block port 25 to prevent worm-type mass mailings. In McAfee for example, you can verify this if you bring up the VirusScan Console and look at the Access Protection Task. Check the properties for the port settings.
You should disable any anti-virus checks on port 25.