How to change attached fax name?

When I receive fax via email in subject and body I have this line:

Fax attached Nº fax000000472.pdf

If I receive new fax, number is fax000000743.pdf and so on…

But attached file name is fax.pdf
How can I change and where attached file name to be just like in subject fax000000472.pdf. Problem is because every time I need to save fax, I have to manually edit attach name.