There is an explanation from Rick about this e-mail some have received concerning the update Newsletter.
With that said., the E-Mail Protocols (believe POP3 supports it,. while SMTP doesn't) where it will send back certain Status information... such-as if an E-Mail was Received, Read, Flagged, Forwarded, etc.
These technically can (although no idea is TGC actually do) track such status feedback for Metric Information.
And keep in mind I'm not singling out TGC... almost no business' I know actually make usage of said E-Mail Features.
That said I don't know of many people who actually read Newsletters., I mean they'll mark them as "Read" but they couldn't tell you what was in them.
Probably because most of the time they're little more than filler information rather than anything interesting.
Again I'm speaking generally not specifically here.