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To merge e-mails for contributions made before the .mailmap was edited or added, you need to specify these emails e-mails in Manage Account - Email addresses for each user.
The easiest way to understand what e-mails should be specified is to find equally named users on the Contributors tab and hover over their names.
You can add as many e-mails as you want, only if they are not used by other Stash accounts.
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