frankiejean,
Thanks for your reply.
To answer your question with the most specific information about Mail Drop, please see the section titled, 'Send large attachments using Mail Drop', in this support article: Add attachments to emails in Mail on Mac - Apple Support.
As mentioned, what you've described with the attachments appearing directly in the body of the email message itself, is expected. What is not expected, is for the receiver to not be able to view the attachment. We have a few more questions to help with this specific issue.
-Does this happen when sending attachments to other Mac users, Windows users, or both? If the issue only happens when sending attachments to Windows users, please see the section titled, 'Send email attachments to Windows users', in the above article.
-If you were to send that same email message, with the same attachment, to yourself, or another personal email account you own, are you able to view the attachment without issue?
-As quoted from the article shared above, "By default, Mail inserts images at their actual size. If different sizes are available, you can choose one from the pop-up menu located on the right side of the message header." If you were to choose a different size, if available, does that help the receiver view the attachment without issue?
We look forward to hearing back from you.