use diagnostics;
m/^de.e++issues@dell.com$/;

__END__

Nested quantifiers in regex; marked by <-- HERE in m/^de.e++ <-- HERE
	issues.com$/ at C:\Perl\toolic\foo.pl line 2 (#3)
    (F) You can't quantify a quantifier without intervening parentheses. So
    things like ** or +* or ?* are illegal. The <-- HERE shows in the regular
    expression about where the problem was discovered.
    
    Note that the minimal matching quantifiers, *?, +?, and
    ?? appear to be nested quantifiers, but aren't.  See perlre.