This tiny script shows the content of the mail queues of multiple servers and give you the possibility to hold, release, delete and reqeue single messages.
In addition, you can also requeue all messages (sendmail -q).
Download the gzip'ped tar archive
$mailservers and $user to your needs/etc/sudoers on the mail server(s), assuming user admin for login to the mail server(s) (change it to your needs):
---snip--- admin ALL=(ALL) NOPASSWD: /usr/sbin/postsuper admin ALL=(ALL) NOPASSWD: /usr/sbin/postqueue ---snip---
http://yourwebserver/mailqmgr/index.php