I assume that everything in an email message is readable by someone else.
We use a secure FTP set up to transfer anything sensitive. simply add the info to a file, say Word, Excel, whatever, it doesn't matter.
The transfer is 256bit encrytped, the data on the server is 256 bit encrypted and the download to the recipient is also 256 bit encrypted. They need to use an agreed password before they can get the download.
No software for the recipient to download, and they can actually send files back to us using the same secure mechanism.
Even better we don't end up with our people using Exchange as a filing system, using system resources and saving cash.