Developer docs can't be found online
README.md says "You can find online developer documentation at http://library.gnome.org/devel/gmime/stable/" but that is no longer true. library.gnome.org points to developer.gnome.org, which has had a major revamp, and no longer includes API docs, so any links to that site are now broken. See https://www.bassi.io/articles/2021/08/01/documenting-gnome-for-developers/ for info on that story.
For some reason, Gentoo chooses to not include those docs in the installed package, so I know I'll have to go digging in the source, unless I can find an online copy. At minimum, any links to that site within the docs or code need to be either removed or changed. It would be great if there were another known online location of all the docs, but that's probably a larger effort for another time.