git filter-branch --env-filter '
an="$GIT_AUTHOR_NAME"
am="$GIT_AUTHOR_EMAIL"
cn="$GIT_COMMITTER_NAME"
cm="$GIT_COMMITTER_EMAIL"

if [ "$GIT_COMMITTER_EMAIL" = "<old email>" ]
then
    cn="<new name>"
    cm="<new email>"
fi
if [ "$GIT_AUTHOR_EMAIL" = "<old email>" ]
then
    an="<new name>"
    am="<new email>"
fi

export GIT_AUTHOR_NAME="$an"
export GIT_AUTHOR_EMAIL="$am"
export GIT_COMMITTER_NAME="$cn"
export GIT_COMMITTER_EMAIL="$cm"
'