Gmail – Preventing Trimming of Identical Email Content

As a bit of a spoiler, we tested this last night. I have two email address (which I will call for the sake of example "test1@gmail.com" and "test2@gmail.com"), and then we did this:

To:      Rebecca <Recip@gmail.com>
From:    My Name <test1@gmail.com>
Subject: this is a test
Body:  blah blah whatever

and additionally

To:      Rebecca <Recip@gmail.com>
From:    My Name <test1@gmail.com>
Subject: this is a test
Body:  this should nest under the other

and voila, they nested. No work required. And then we did this:

To:      Rebecca <Recip@gmail.com>
From:    My Name <test2@gmail.com>
Subject: this is a test
Body:  does this nest with the others?

And it didn't nest!

So in other words, two emails from the same sender with the same subject will nest. Two emails from two different addresses with the same subject will not nest.

On Android:

1. Open the Contacts application
2. Press the MENU key then Accounts
3. Click on your Gmail account
4. Uncheck Sync Contacts

Then in a web browser:

1. Open Gmail
2. Go to the Contacts workspace
3. Delete all contacts, page by page.

Gmail will still expand in the Android app, but there at least you can modify the To: line manually.

(Huge thanks to derobert for the tip!)

Related info: https://support.google.com/mail/answer/1311182?hl=en