my @sorted_ids = sort {$mailarray{$a}{"from"} cmp $mailarray{$b}{"from"}} keys %mailarray;

##</code><code>##

$mailarray{$msgid}{"to"} .=
    (exists $mailarray{$msgid}{"to"} and length $mailarray{$msgid}{"to"} ? " " : ""). $to
    if ($msgid, $to) = ... # your regex here