[imp] IMP 4.1 - Where is the "Message Source" link?

[Jess C.]

First off, congrats on all of the latest Horde releases! I upgraded our 
environment last night, and everything is running smooth.

I have one minor question that makes me feel a little silly to ask.. 
After upgrading, I can't find the "Message Source" link in IMP anymore 
when viewing a message. I've looked through Horde and IMP's configs and 
options, and just can't see anything to turn it on. Did it get removed 
in this release, or am I just plain overlooking it somehow?

Thank you,

Jess