Does running with -X provide any clues? Have you tried the same settings in another app?
As an aside, I wouldn't send email from Maven itself. I'd have Jenkins fire off the build and send an email after it was completed. That way only official builds would result in email notifications. Or just let interested parties subscribe to the RSS feed for the job in Jenkins. Or they could subscribe to the RSS feeds in Nexus (which is where we deploy our artifacts).
You will have to contact your IT department to find out the proper settings for connecting to the corporate email system. I have the same issue with the Exchange server in my company - I cannot programmatically access the same Exchange server that I access via Outlook. Instead, there is different server that was set up to handle programmatic connections, and I have to target that one.