If you don't mind the extra step of removing the trailing comma then a hash should work: 

my %hash;
while ( <> ) {
    my ( $dept, $email ) = split /:/;
    $hash{ $dept } .= "$email,";
}

s/,\z// for values %hash;

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In reply to Re: Best Way to Map Data by jwkrahn
in thread Best Way to Map Data by walkingthecow

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