P. Keenan said:
Called MsgTag - it tells you when any mail you send has been opened at
the other end.
Privacy issue follows: if you don't care about same, there's nothing to
see, here.
To get around the "normal" way of handling read receipts[1], wherein the
recipient has to have receipts enabled in his email client (or have it
set to pop up a dialog asking if he *wants* to send a receipt, when he
opens an email that requests one), these guys are using HTML.[2] This is
from fairly deep into their support structure:
"A small number of email users have text-only email clients, which do
not trigger tagged messages due to the fact that MSGTAG relies on an
embedded image in the tagged message. Some email security products
designed to filter out spam and viruses also inadvertantly block the
tags produced by MSGTAG."
I found that in a discussion about why it won't work with Pegasus mail.
http://www.msgtag.com/support/faq/#pegasus
All in all, those security products aren't "inadvertantly" blocking this
stuff. They're doing their job.
[1] I presume the "normal" receipting method revolves around the use of
the Disposition-Notification-To header.
[2] Another reason for email clients not to be rendering HTML.
