Search observation:
During an extended operation (eg: deleting hundreds of messages) one is not able to execute another search from a folder view until the in-process operation is complete. Search clocks until canceled or the first operation completes. No complaints there; app is behaving as expected.
However, I recently discovered one can initiate a secondary search from the account ("home") panel under the above conditions which effectively permits multi-tasking search operations. Yippie!
I did not try to queue up another set of tasks (eg: a second wave of message deletes); no need to push the envelope.
I should also note in-app navigation/reading/composing/etc. was never inhibited with background tasks operating; only the search function was impacted.
Again, no complaints - just sharing a new found capability!
ps: Yep another edge case no one else cares about (lol).