When I send a file to the recipient he can't open it

I have a dropbox
In the past, I simply dragged the file from the application to email and sent it to all kinds of recipients and they all managed to open the files.
Today when I do the same action they receive the file attached to the email but cannot open it
If I share the link of the file, what is DROPBOX, they click on the link, download the same file and it opens for them
Why did it change and how can I solve the problem?
It should be noted that I drag the file to the email after it has a green mark on it that it has made a backup
It should be noted that I can open the files freely and I don't get any error message
It should be noted that the recipients receive various messages regarding an error in opening the file or that the file is corrupted or that the file is not in a certain format!
I would appreciate help because all the stupid DROPBOX staff say that this is not a problem related to them, although it is definitely something related to them