Lotus Notes has had “click and drag” selection for more than a decade. If there is any way to sort those emails (i.e., by name, by date, by subject, by size) you can go into the “All Documents” view, sort by that column, and simply click and drag down the list. It will select all those documents which can then be deleted at once. Even if you can’t do that entirely, if you can group the emails and then select sections, you can similarly select a bunch of emails and then delete them all at once.
CAUTION: One of the most common ways I know of for a user to either delete or move emails they did not plan to delete or move is to change operations while they have a lot of documents selected. Most commonly, someone selects a lot of documents to move and, while doing that, sees a document they want to delete. So they stop where they are and hit “delete” on that document. Unfortunatly, Notes does NOT see this as a new action, and deletes EVERYTHING the user previously had selected. If they are smart enough to realize this, or are not a clean-up type who empties the trash immediately, they’ll be okay. If they get too efficient and empty the trash, you have to go to a backup to get the documents back.
As for performance issues, one of the things we do is run a server-side compact on all files and update the views every night. We also automatically delete anything that’s been in the Trash for 48 hours. I’ve never used SaveNSync and we do not use third-party software in the companies I’ve worked in — Notes has always had all the tools we needed.