We recently had an issue, where the Queued messages folder kept growing with number of "pending " messages and emails stopped for nearly 12 hours.
Everything from SMTP to Daemons was checked and we found no specific pointers to why this issue occurred.
We restarted the e sourcing system as a last resort and everything turned fine, 0 Queued 100% processed messages status "Sent"
Any clues, so as to why this issue occurs??