I just did a new Beta version of my shipping App and want to distribute it to Beta testers. EDIT - This was my mistake in receipt parsing

I have some local mail folders (mailboxes) that are from an old email account that are kept locally on my Mac. The account is still configured, but "offline". It has transferred through many hardware and software upgrades over the years. I can still view the mailboxes using Mail App and read all the messages. I want to give a copy of all of the messages in a bunch of these mailboxes to someone else. I have recently discovered that when I "Export" a mailbox, the Mail App does not include any messages that contain an attachment. If I select one of these messages and then "Copy" it to another mailbox, eg: "On My Mac", only the headers are copied and the message body is blank and there are no attachments. If I do the same thing with a message with no attachment, there is no problem. I need to find a way to get all of the messages out of these mailboxes so that I can give them to someone else for review. If I look, I can find the .emlx file under ~/Library/Mail/V9/"etc"/OldMailFolder.mbox/"etc"/Messages and the attachment in the Attachments folder. Again, I can read/view all the messages in the folder. So I know all the needed information is there, it's just not being exported or copied. Does anyone know if a different email client would work? If so, which do you recommend? Or can you suggest a work around? Or is there another tool that might do the job of properly exporting a mailbox? Do you think it would make a difference if I did all the work to take the email account back online? Mail version 15.0, macOS 12.2.1

I have a macOS App that uses a custom file format (XML based). It is properly in the Info.plist as a file format so that my App is launched when this custom file type is double clicked etc etc. All that has been working fine for awhile now. If I use Finder and duplicate one of these custom files, it does the right thing and creates a "File 2.customxml" file, keeping the file extension intact. But if I AirDrop one of these files to another Mac and there is already a file of the same name in the Downloads folder, it creates the file "File.customxml 2" instead of "File 2.customxml". And of course there is no Application registered to open a file of type ".customxml 2". If a user clicks "Open" in the AirDrop popup, my App is opened with this file the first time, but not opened or informed the second time and instead it falls to another App, eg: TextEdit Is there anyway I can get AirDrop to do the "right" file naming? (This is all between 2 Macs)