How do I check the postfix queue size?

Or, less typing:

mailq

postqueue -p

qshape active

will show you the number of emails being sent to each domain and how long they have been in the active queue

qshape deferred 

will show you the same but for the deferred queue

Here's what I use, culled from the postfix mailing list. I removed the author's name, in case he doesn't want it here (you can see it at the source). It only displays totals.

#!/usr/bin/env perl

# postfix queue/s size
# author: 
# source: http://tech.groups.yahoo.com/group/postfix-users/message/255133

use strict;
use warnings;
use Symbol;
sub count {
        my ($dir) = @_;
        my $dh = gensym();
        my $c = 0;
        opendir($dh, $dir) or die "$0: opendir: $dir: $!\n";
        while (my $f = readdir($dh)) {
                if ($f =~ m{^[A-F0-9]{5,}$}) {
                        ++$c;
                } elsif ($f =~ m{^[A-F0-9]$}) {
                        $c += count("$dir/$f");
                }
        }
        closedir($dh) or die "closedir: $dir: $!\n";
        return $c;
}
my $qdir = `postconf -h queue_directory`;
chomp($qdir);
chdir($qdir) or die "$0: chdir: $qdir: $!\n";
printf "Incoming: %d\n", count("incoming");
printf "Active: %d\n", count("active");
printf "Deferred: %d\n", count("deferred");
printf "Bounced: %d\n", count("bounce");
printf "Hold: %d\n", count("hold");
printf "Corrupt: %d\n", count("corrupt");

EDIT: Fixed a typo on line 26.

postqueue -p | tail -n 1

Last line in the postqueue -p shows how many requests and size:

-- 317788 Kbytes in 11860 Requests.

[root@server ~]# time mailq | grep -c '^[0-9A-Z]'

10

real 0m1.333s

user 0m0.003s

sys 0m0.003s

(above result indicating that there are 10 email is queue)

If you don't have qshape you can install it via the following yum commands:

yum groupinstall perl development
yum install postfix-perl-scripts

qshape prints Postfix queue domain and age distribution information. You can read more about it here:

http://www.postfix.org/QSHAPE_README.html

Example output

% qshape -s hold | head
                         T  5 10 20 40 80 160 320 640 1280 1280+
                 TOTAL 486  0  0  1  0  0   2   4  20   40   419
             yahoo.com  14  0  0  1  0  0   0   0   1    0    12
  extremepricecuts.net  13  0  0  0  0  0   0   0   2    0    11
        ms35.hinet.net  12  0  0  0  0  0   0   0   0    1    11
      winnersdaily.net  12  0  0  0  0  0   0   0   2    0    10
           hotmail.com  11  0  0  0  0  0   0   0   0    1    10
           worldnet.fr   6  0  0  0  0  0   0   0   0    0     6
        ms41.hinet.net   6  0  0  0  0  0   0   0   0    0     6
                osn.de   5  0  0  0  0  0   1   0   0    0     4

Here is an example.

#!/bin/bash

for q in active  bounce  corrupt  defer  deferred  flush  hold  incoming  maildrop  pid  private  public  saved  trace

    do
        count=$(find /var/spool/postfix/$q ! -type d -print | wc -l)
        echo $q $count
    done