Ive found couple of messages that were different sender names somehow interjected...in a long “list” of messages by the “same” sender and this has slowed the process down somewhat
example
abcauto
abcauto
abcauto
B+H
abcauto
abcauto
had i grabbed everything Id initially selected for deletion..I would have deleted one message I wanted to save.
I needed this lesson in housekeeping I guess.
Sender search not sender sort. That should yield only that sender.
I suggest putting quotation marks around your search criteria and see if that helps limit the responses.