use Fcntl qw(:DEFAULT :flock :seek);

sysopen FILE, $mailclicks, O_RDWR | O_CREAT or die "couldn't open $mailclicks: $!";
flock FILE, LOCK_EX or die "failed acquiring lock on $mailclicks: $!";

my @records = <FILE>;

seek FILE, 0, SEEK_SET;

for(@records) { # now the line will be in $_ rather than $rec
    next if $_ eq "\n"; # skip empty lines completely
    my ($id) = split /::/, $_, 2;
    ++$received if $id eq $formdata{id};
    print FILE $_;
}

truncate FILE, tell FILE;
close FILE;