Sometimes you are reminded that you didn't document something you thought you did. Turns out that I wasn't even the one to write this up the first time but Gary did while he was on the team (since moved to ISA support).

As of October 11, 2005 all EASI* Passport domains are fully supported for the Public
IM Connectivity (PIC) Service. We also refer to these as Vanity domains in case you hear the term.

This means that Microsoft Office Communicator users can communicate with MSN users
using EASI Passport IDs through PIC. EASI ID allows MSN users to create an IM
address through Passport using the domain name of their choice.

For example a user’s EASI Passport ID could have been username@contoso.com
<mailto:username@contoso.com>. This is a great service for MSN users but this
caused problems once PIC enabled users tried to communicate with them through
Office Communicator.

With this change, the EASI Passport ID can be used with PIC by making a simple
change when adding a user to your Communicator contact list. A Communicator user
that wants to add the EASI Passport ID of username@contoso.com would simply add the
following address to their search field: username(contoso.com)@msn.com

This increased the effectiveness of the PIC service as you now no longer need
contacts with unsupported EASI Passport domains, to change their domains in order
to use the PIC Service.