.mailmap file ==> Name you want to keep <email> Name you no longer want <email>

John Doe  John Doe
John Doe  John Doe
John Doe  john doe
Max Example  Max
before
$ git shortlog -se
     1  John Doe <John@Doe.org>
     1  John Doe <John@doe.org>
     2  John Doe <john@doe.org>
     1  Max <max@test.co.uk>
     3  Max Example <hi@test.com>
     1  john doe <john@doe.org>
after
$ git shortlog -se
     5  John Doe <john@doe.org>
     4  Max Example <hi@test.com>