This is something we recently started doing. If email sent to your email address bounces with an error message like, "This email address doesn't exist", then your email may eventually be changed to u...@bounces.invalid. (It's not possible for users to change their email address to something ending in .invalid, so this can only be an administrative change.) Because your old email didn't exist, somebody could've registered your non-existent email address and used that to steal your account.
I didn't particularly intend for the trust warning to appear for these automatic changes, but it's a niche situation and a bit difficult to fix, so I probably won't fix this unless several other people complain. It only lasts 30 days, after all.
It's a nice touch actually! particularly for inactive account policy some email providers have. I could see some members creating an email account solely for bitcointalk then forgetting to log back for a year or two so their account gets removed due to being inactive.
I wonder if op was using gmail? because google has recentry started deleting inactive accounts:
When your Google Account has not been used within a 2-year period, your Google Account, that is then deemed inactive, and all of its content and data may be deleted.
... December 1, 2023 is the earliest a Google Account will be deleted due to this policy.