$file = "ex1.pl";

open(MAIL, "$file") || die "cant open spool\n";
@array = <MAIL>;
close (MAIL);

foreach $line_num (0 .. $#array) {
    chomp($array[$line_num]);#prepare for m//
    if ($array[$line_num] =~ /^\s*$/) {#a blank line
        foreach (1 .. 3) {
            print $array[$line_num + $_];#remember those are not chomp'd
        }
        last;#without this you will see the warning about uninitialized values you saw
    }
}