As reported by Bob Bib (10/7/2018) via email discussion list
http://lists.bcn.mythic-beasts.com/mailman/private/mutopia-discuss/2018-October/001002.html

Well, according to the start page, there're 2 mirrors:

1. Canada (main): http://www.mutopiaproject.org/
2. Portugal: http://eremita.di.uminho.pt/mutopia/

It turns out that currently Portuguese mirror is serving web pages only,
and all the music content is loaded from the main mirror,
and I wonder whether it should be that way.

E.g. You can view info about the Blue Danube Waltz on both mirrors:
http://www.mutopiaproject.org/cgibin/piece-info.cgi?id=519
http://eremita.di.uminho.pt/mutopia/cgibin/piece-info.cgi?id=519

But when you try to download MIDI, you have the same link on both pages:
http://www.mutopiaproject.org/ftp/StraussJJ/O314/blue_danube/blue_danube.mid

Out of curiosity, I've tried to guess if we can download the music files
from the Portuguese mirror,
and it looks like the answer is positive -- here is the guessed mirror
MIDI link:
http://eremita.di.uminho.pt/mutopia/ftp/StraussJJ/O314/blue_danube/blue_danube.mid

--
Best wishes,
Bob