MultiPing doesn't create Mime-type messages, just plain email text.
Can you clarify on how you're seeing Mime-encoded messages?
Here is the body of an alert I just had fire (I removed some of the non-relevent headers).
<BEGINNING OF MESSAGE>
From: "MultiPing" <email@example.com>
Subject: MultiPing Auto-Alert!
Sender: MultiPing <firstname.lastname@example.org>
Date: Tue, 11 May 2004 12:45:35 -0600
X-Library: Indy 9.00.10
A MultiPing alert has fired, for the following period:
5/11/2004 12:45:15 PM to Current
Monitoring: 188.8.131.52 www.pingplotter.com
Repeated every 1 second
5/11/2004 12:45:15 PM *
5/11/2004 12:45:16 PM *
<remainder snipped - repeating of the same type of text>
<END OF MESSAGE>