Anyone who tells you that email propogation is instantaneous should consider this Received trace:

Received: from X.Y.edu
        by sunset.backbone.olemiss.edu (8.12.10+Sun/8.12.9) with ESMTP id i38G1LAf017356
        for <cnlawren@olemiss.edu>; Thu, 8 Apr 2004 11:01:21 -0500 (CDT)
Received: from a.b.c.d
        by X.Y.edu (8.12.9-20030924/8.12.9) with ESMTP id i36JvaK3027962
        for <cnlawren@olemiss.edu>; Tue, 6 Apr 2004 14:57:37 -0500 (CDT)

In other words, the email took 44 hours, 4 minutes to get here (well, 44:08 if you count the 5 minute fetchmail cycle on my inbox). I probably could have gotten a paper letter sent first class from X.edu (within a day’s drive in a neighboring state) in less time.