The issue of deadnaming aside, turning on log.mailmap by default is
the sensible thing to do given that other Git features already honor
it that way.  Having it ignored-by-default (but only sometimes) just
adds confusion when a mailmap is available.

quoted

quoted

 - The '.mailmap' provides a list of transgender individuals, along
   with their deadname, which can be used to harass them.

This is potentially a problem but it's not as bad as you depict.  A
mailmap rule can match against e-mail only, which is precisely what I
have done in my projects.

Ah, I may be severely mistaken -- my memory was that '.mailmap'
rewriting could be used to rewrite both name and email, not merely
email. I thought that records could take:

  A U Thor [off-list ref] -> B C Xyzz [off-list ref]

instead of canonicalizing by email alone. If this is the case, then I
completely agree and share the opinion that this is not as bad as I
originally depicted.

The long form you give there is to be used in case the old email
address is not a unique key. See 'git help shortlog'.

The problem we have at work is that one woman's old email address
includes her deadname, like [off-list ref].  I will
leave it up to her whether she chooses to be listed explicitly in the
mailmap.  I have wondered if we should permit hashed email addresses
to be used for this specific case, but this also has its drawbacks.

Phil