I recently came across a peculiar situation for the first time: a person not affiliated with Applicant filed a correspondence change with the USPTO via TEAS. The only change was to add an additional email address to the record. They did this just before the registration issued.
My suspicion is that this was an effort to game the Amazon Brand Registry system, which generates a link emailed to the trademark registration email address(es) of record when creating a new account.
I filed via TEAS to change the correspondence to remove the email; and then a few days later the same email address was used to do it a second time. To add to the challenges, the email address used is from a secure private email domain (tutanota.com).
My client and I have reached out the USPTO (who has responded quickly, I am pleased to share!) and to Amazon to warn them about this. I suspect it has happened to others who may not be aware.
If anyone has any additional information or experience about this issue, please share in the comments.