We had whole emails being distorted/broken by the T-Online browser client for years., too.
The initial solution was to place a "view in browser" snippet stating "If the email is no...
Another idea that comes to mind could be to trigger a webhook on form fill, that checks the fields filled by the form against whatever you define as success or failure in the webho...
Stumbled over the same question's wording.
As of quote from the comments: "priority of the segmentation is Celery > Beets > Broccoli > Carrots"
This is not stated in the question....