I've been using Pegasus Mail since circa 1980's [Currently WinPMail version: Version 4.80.1028, Jan 16 2022, build ID 1028]. For some reason, just noticed recently, "Selective Mail Download" is not working properly as follows:

Whenever I try to retrieve more than 10 emails, I only get 10? Examples follow:
Using "File/Selective Mail Download/Make It So"

1. Attempt = Delete 41 and retrieve 35, Result = retrieves 10 of that 35, and none are deleted.
2. Attempt = Delete 81 and retrieve 0, Result = All 81 are deleted.
3. Attempt = Delete 0 and retrieve 94, Result = retrieves 10 of that 94.

This is bizarre?? Has anyone else experienced this issue? Any insight would be greatly appreciated.

Did you check with your provider whether they impose some kind of new restrictions?

Next thing to try would be session logging to be enabled on Tools > Internet Options > General, for using it please check PM's online help under Contents > Internet Session Logs. Please be careful with posting any log output here because it will contain your user name and password in an easily decodable encoding!

In the POP3 host definition Download controls tab is an option where you can specify that max number of messages to download. Might that have been inadvertently set to 10?

Bingo!! I'm not sure how that setting got changed, BUT, it was set to 10... It was the "default" POP3 definition. Possibly reset when I upgraded versions, but that's pure speculation? Other POP3's were not affected. And, it seems that setting this to zero is the same as infinite... It was a real bear retrieving and deleting only 10 emails at a time. Thank you! Your input is greatly appreciated. I'm back to the Pegasus I love...