use strict;
use warnings;

my $addr_pattern = qr/\s*?(?:\w+\.?)*\@(?:\w+\.?)*\s*?/;
my $name_pattern = qr/(?:(?:\w+\s+)*\w+)/;

my @valid_patterns = (
    qr/$addr_pattern/,
    qr/$name_pattern\s+<$addr_pattern>/,
    qr/<$addr_pattern>\s+$name_pattern/,
);

my $all = join '|', @valid_patterns;

while (<DATA>) {
    chomp;
    my ($addr) = /^(\s*?($all)),?/;
    print "$addr\n";
}

__DATA__
Xung03 <xung03@aol.com> To: xung03@aol.com From: ...
xung03@aol.com To: xung03@aol.com From: ...
<xung03@aol.com> Xung03 XMS To: xung03@aol.com From: ...
<xung03@aol.com> Xung03 XMS, To: xung03@aol.com From: ...
foo_bar@aol.com
Xung 03 <foo_bar@aol.com>