Example: I recently (2 months) received, say, 150 e-mails from one person. During that same period, that person has also received lots (~300) of e-mails that are in my client: ones I sent, ones they were CC-ed, etc.

Now, I need to find that pdf they sent me some time ago. It would be no problem to scour the 10 or so message I received from this adress with a pdf attached (still doable without the mimetype).

TB lets me search messages that "concern" that person, but also gives me the ones they didn't send. Would a "sent by" be too hard to provide? Quick search works a lot better than the regular search for this, it's something I do multiple times a day. I sometimes spend more than 5 minutes looking for an e-mail, then give up, load zimbra, and I'm able to find the e-mail in 10 seconds thanks to the more granular filtering available there.