Mail command - change filename when is attached

Question

I'm trying to send a mail with an attached file. I'm using mailutils to send mail. The command I use is the following:

mail -s "Hello World!" -r "[email protected]" "[email protected]" -a cc:"[email protected]" -A "/opt/app/whatsup.txt" --encoding=base64 -A "/opt/app/hello-world.txt" --encoding=base64 <<< "Hello World 122345"

For the file, I have to indicate the path from where to get it, for example I'll use /opt/app. The mail is sent successfully. However, upon review, I am surprised to find that the file is named after its local location. I have to tell it its folder because if I don't, the command recognizes it as being at the root address

Is there a way to change the name of the file without having to remove its location from where to send it?