[CentOS] clustered mail server?

[Christopher Chan]

>> No, mail spools/queues do not need replication. Stuff in the queue are 
>> usually deleted in a second and such dynamic change is not worth 
>> replicating. If you do put the queue on a distributed filesystem, in 
>> most cases you cannot have more than one instance running save for 
>> sendmail.
>>
> 
> outbound mail can sit in queues retrying for hours negotiating their way 
> into the greylists of the likes of Yahoo.    I guess if you don't mind 
> the possibility of messages getting lost around a server failure event, 
> then its no big deal, for sure.
> 

That only leaves putting the queue on a distributed filesystem. 
Replication will not be a complete solution to that and qmail queues 
cannot be replicated.

Then there is the question of whether to leave a message in the queue 
for more than 4 hours given the expectation of email to be more or less 
instantaneous.