Gmail – Restoring all messages of a thread in Gmail at once

The following conditions must be met:

1. The subject must be similar (e.g. test and re: test will work; but test and test 123 won't).
2. The sender must be a part of the thread OR the in-reply-to header must be used.

The in-reply-to header can be used via Gmail's interface by simply replying to the thread. This is what enables forwarded messages to be a part of the same thread even though the sender is different.

If you want more information, you can check out my blog post where I posted more detailed information about my findings.

Try with first disabling Ad-block. Or with

• Open Adblock preferences from Tools

• Adblock Plus Preferences [Ctrl-Shift-O] and make sure your Filter Subscriptions are up to date.

And to resolve the issue for Apple Mail go to email account settings and change your user name to @gmail.com.

Hope this helps.