my $address_exists_sth;
sub address_exists {
   my ($address) = @_; 
   $address_exists_sth ||= $dbh->prepare('
      SELECT * FROM emails WHERE `email`=?
   );
   $address_exists_sth->execute($address);
   my $rec = $address_exists_sth->fetch();
   $address_exists_sth->finish();
   return $rec && 1;
}

for my $address (@addresses) {
   if (address_exists($address)) {
      ...
   }
}
[download]

Update: DBI can already do some of the work for us:

my $address_exists_sth;
sub address_exists {
   my ($address) = @_; 
   $address_exists_sth ||= $dbh->prepare('
      SELECT * FROM emails WHERE `email`=?
   );
   return $dbh->selectrow_arrayref($address_exists_sth) && 1;
}

for my $address (@addresses) {
   if (address_exists($address)) {
      ...
   }
}
[download]

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