Gmail uses the email subject of a message to decide if it should combine related email messages together into a thread. Using thread splitter, you can separate these email threads into parts.
Once you activate the interface, you are given the option to select specific emails you want to move into a new thread. After selection, you can give these emails a new subject line. The emails will then be permanently removed from the original thread and moved into their own thread.
There are some important notes and caveats that you should know about before using this feature:
Splitting a thread cannot be undone. Be sure you want to split the messages before confirming the separation, as it is impossible to join them again.
The new thread will be dated to your current time. We create a new thread in Gmail for these messages and cannot backdate it.
How to use the thread splitter
If you're ready to use the thread splitter, first open the email you're looking to split:
Click into the three-dot More menu from the email toolbar
Select the final option Split Thread to begin
All messages but the most recent in the thread will become available to select in a collapsed state
Check the box next to each message you would like to split
After selecting the messages you'd like to split, confirm the selection by clicking Move Messages to New Thread.
Enter (or confirm) a subject for the new thread and select Done.
After confirmation, you will be brought back to your inbox where the thread will be at the top.
Note: Thread Splitter is not compatible with the 'Preview Pane' setting in Gmail. Please temporarily turn off Preview Pane if you wish to split a thread.