I'm having a hard time understanding why we should queue messages for so long. Doesn't that just confuse the end users when their message disappears into a queue for 4 or 5 or 7 days? Especially when they are expecting the message to get there in 3 minutes (or maybe even "instantly")?
I've tried to come up with "horror story" scenario where having a short queue lifetime could cause problems that end users would blame the SMTP server administrator for. I haven't been very successful. Here's the best I have:
- Someone mis-configures their mailserver's DNS with a TTL of 86400.
- An account on our server gets compromised and used to send spam. We get blacklisted on a DNSBL. (Would that even be seen as a temporary failure? Or is that seen as a permanent failure?)
It seems like anything I can come up with where a remote server is actually down, one of our users getting a bounce would be happy to blame the remote server admins instead of us. And, it seems like an end user might even appreciate getting a bounce instead of having their message "disappear" for a couple of days.
I have heard of greylisting, but my understanding is that is for a short time, maybe a max of 15 minutes of delay.
What would be the harm of having a queue lifetime of ~ 12 hours? Or even 6 hours? What good reasons are there for 4+ day queue lifetimes? Or is it just Cargo Cult system administration?