Assuming too that all your emails were in an array, it is even simpler to let perl do most of the work:

%hash_of_unique_emails = map { $_ => 1 } @array_of_emails
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Or even better, as a one liner from the shell:

perl -e 'print keys %{ { map { $_ => 1 } <> } }' < test.data
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That should work on windows too (worked fine on my OS X machine, but alas, no windows box to test it on here).

-stvn

update intially forgot the map {} in the first example ,.. sorry been a long day,..