You can currently find me twice in https://thanks.rust-lang.org/rust/all-time/

That's because at some point I have switched to capitalizing my e-mail (address similarly to my GitHub's username).

man gitmailmap(5) explicitly states¹:

Both E-Mails and names are matched case-insensitively. For example this would also match the Commit Name <commit@email.xx> above:

Proper Name <proper@email.xx> CoMmIt NaMe <CoMmIt@EmAiL.xX>

Similarly, git shortlog seems to properly group both capitalizations of my e-mail address under the same author/commiter.