Yes, your original statement is correct concerning sending secure emails from a company's mailserver.

One option you have is the Cisco Registered Envelope Service(CRES), that is handled by Cisco Systems and Ironport Systems.

The sender of the email needs to get registered first, but once they're registered they can send secure emails by going to https://res.cisco.com

Here are some articles that explain how CRES works and some FAQ's:

1. https://res.cisco.com/websafe/help?topic=RegEnvelope

2. https://res.cisco.com/websafe/help?topic=FAQ

My company wants to provide a way for external users to send secure mail to us.   

My understanding is that the IronPort Secure E-mail solution is only for Outgoing mail, is that true?

If so, what are some of the solutions that we could/should evaluate?

THANKS.