Please use code tags for legibility. Fortunately I get proper indentation when I quote your message so it's not completely unreadable.

Code:

use locale;
use DBI;
use Cwd ;

You don't seem to be using the DBI stuff or Cwd; also doubtful what the locale is for. The logs don't use locale-dependent formatting, do they?

Code:

foreach $myQID (keys %sender_emails)
{
        $myto = $recipient_emails{$myQID} ;
        $myfrom = $sender_emails{$myQID} ;
        $tocount = $recipient_count{$myQID} ;
        next if $tocount >= 6;
        foreach $rcpt_group (values %sender_emails)
        {
                ($1, $2, $3, $4, $5) = split(/\s+/, $_);
                @rcpt = ("$1", "$2", "$3", "$4", "$5");
                {
                        foreach $rcpt (@rcpt)
                        {
                                print $myfrom . "," . $rcpt . \n;
                        }
                }
        }
}

You can certainly defer all processing until you have read the whole log file, but like I suggested earlier, it might be more memory-efficient to process and forget queue entries as you see them, assuming that "removed" is a good pattern for seeing when you have a full entry.

Assigning to $1 $2 etc seems wrong, I guess you might be able to do it but that's definitely not recommended. Why don't you assign the result of the split directly to the list @rcpt anyway? If you want to restrict it to just five fields and throw away the rest, you can restrict the split, or splice away the remainder after splitting. And I guess you want to be splitting $rcpt_group, not $_.

Better yet, collect the formatted output already in the initial loop, and just don't print it if the count is too large. I wanted to avoid having two variables and needlessly collect information which was not going to be printed, so I used references to lists instead, but this is certainly a workable solution as well.

Using the string join (dot) operator on a string just for printing it is mildly inefficient, you can just print a list without first gluing together its elements into a single string.

You need to double-quote the \n to make it into a newline; as it is, it's a reference to an undefined symbol (you should have used strict after all!) with a blank print value; that's why you aren't getting any newlines in your output.

To reiterate, that's basically as if you had has an identifier UNDEFINED_SYMBOL and used a backslash to produce a reference to it: \UNDEFINED_SYMBOL. Perl is unacceptable forgiving about these things when you don't use strict and use warnings, for legacy reasons -- you should always use strict and use warnings for new scripts (I wrote "nontrivial" scripts but all scripts appear trivial when you start optimistically working on them). I confess that I too sinned against this -- much against my better conscience.