To ensure better control, I suggest - first, create a folder in the IMAP account for the transfer - second, I recommend highlighting messages and use the COPY to menu option - NOT the MOVE option

I say this because IMAP was not designed for high volume uploads. by creating a new folder on the account and using COPY, you are protected in case the copy fails or is only partially successful , as you will still have all the original messages. People do this regularly; it just needs a tad of oversight. :)

There are different ideas on doing this, so you may see others' suggestions.

Wow, I'm impressed! It works! The only minor sharp edge is that when the messages appear at the new server, there's a paperclip icon signaling an attachment which the messages didn't have, but when I click on the message to read it, the paperclip vanishes. Thank you!

Life is sometimes easy! I was glad to assist. :)