Postfix maintains queues, the pending mails queue, and the deferred mail queue,the deferred mail queue has the mail that has gentle-fail and should be retried (Temporary failure), Postfix retries the deferred queue on set intervals (configurable, and by using default 5 minutes)
To display the listing of queued mails :
postqueue -p
To Save the output of above command :
postqueue -p > /mnt/queue-backup.Txt
Tell Postfix to procedure the Queue now
postqueue -f
