[CentOS] clustered mail server?

Sun May 18 22:50:43 UTC 2008
Karanbir Singh <mail-lists at karan.org>

Christopher Chan wrote:
> I am sorry but I do not share that view for incoming mail. The latency 
> in getting the mail replicated probably is longer than it takes to do 
> the actually delivery to the mail store.

I am not sure what you mean by the word 'replication' but in most cases 
the user mail stores are on the same shared block device. And I've 
worked with an ISP recently that deliver between 12 to 16 million emails 
per day and dont have this problem of 'latency in replication'. Using 
exim and cyrus-imapd over 2 user facing nodes.

>> Besides, as John already pointed out, emails in the spools can hang 
>> around for days. I believe most MTA's only discard completely after 
>> 7days of non delivery.
> That default setting is no longer applicable today. Users will scream if 
> they find out that their mails have been sitting in the queue for a day. 

Mail will wait with a delay if there is a problem with the remote end 
receiving the emails. Users will screan much more if they find that 
their emails are just going into /dev/null and they are having to work 
the retry mechanism by hand rather than their email server. Besides, if 
I send an email at 2am and there was a network outage at the remote end, 
its nice to know that

> For today's businesses, one day can make or break a deal and so email, 
> being a much faster form of communication than snail mail, has come to 
> be seen as the preferred choice. People start calling when they know 
> they are supposed to get an email in a minute or so when it does 
> materialize.

Your point is well made, however - email does normally go in a single 
stream. Its when there is a problem and a retry mechanism hasto kick in 
that there is a problem. Its only the crazy goons who develop MS 
Exchange who havent got their head around this problem, something solved 
by the general internet users about 25 years back.

> He is welcome to replicate the queue. His traffic levels will be so low 
> that it really does not affect things but if he is using qmail I hope 
> that the filesystem is completely identical on the secondary.

I personally hate qmail, its place is back in the 1990's - perhaps in 
the 1980's. But that is a pure personal opinion. I know there are plenty 
of people, some whom I even respect technically, who still use it :/

Also, you seem confused about the filesystem on the secondary. Its not a 
different filesystem - its the same shared block device exposed to both 
machines. if the primary fails, its the same system that the secondy 
see's when its made live. the DRBD packages are included in CentOS - you 
should give it a try. One easy way to do this is setup 2 VM's and have a 
play there. its quite cool.

Karanbir Singh : http://www.karan.org/  : 2522219 at icq