Sending to many multiple email servers

[William Burns]

Egil:

Wow, that's quite a setup.
I'm not understanding the roles of each server in this example, though.

I assume that your 4 mailscanner machines do not host mailboxes. That 
would make them mail relays, and/or mail gateways. (same thing in many 
cases)

I assume again that your 20-25 mail servers ARE your mailbox machines. 
(firewalling them makes a lot of sense) I don't know what your 2 
gateways are for. I guess that they are non-mailscanner gateways for 
people who don't want that service. I'm also not sure what your perl 
script is accomplishing.

Anyway, having balanced MX records pointing to 2 mail relays running 
MailScanner is a great way to load-balance MailScanner. My problem w/ 
such a large mail system is how to achieve load-balancing on the mailbox 
side. Failover is possible w/ something like DRBD, to mirror a 
filesystem between two computers, and then provide IP-address takeover 
if one machine dies.

Another good feature that I'm using is LDAP lookups in sendmail.
w/ LDAP enabled sendmail/mailscanner gateways, I can have mailboxes for 
some users at mydomain.com on one server, and other users at 
mydomain.com on another server. This way, I can have a large 
organization w/ the one domain name, but w/ mailbox servers all over the 
place.
You can also call this mailbox load balancing, but each individual 
mailbox is still hosted by a single machine, so this technique doesn't 
provide failover on the mailbox side.
One great benefit of this approach is that no matter how many gateway 
machines I have, they all have access to the same list of valid user 
names. If someone sends mail to a non-existant username, the gateways 
can deny delivery up-front, and never accept the mail.

-Bill

Egil Fujikawa Nes - Webdeal AS wrote:

>Last weekend we had a test system with 2 mailgatways 4 mailscanner
>servers and around 25 mail servers up. The situation is that I will
>close all my mailserver from being public open on port 25. Some of our
>customers have mailscanning and some don’t. We have servers on two
>different locations and one mailgatway, 2 mailscanners and around 10
>mailservers on each location. As backup for the mail that is going to
>the first location we have the second location and posit.
>
>We was trying many solutions on the transport from the mailgatway to the
>mailscanners, we wanted a failover and load balancing system. One of the
>solutions we making a virtual catch-all users that pipe all the mail to
>a perl script and send the mail from the perlscript, this was not
>working well on heavy load.
>
>We was ending up with a own name server for the two mailgateways where
>we used normal MX record on each domain, those domains that was going to
>have mailscanning got two MX records, both with 10. So then in normal
>use it is going around 50 % of the domains two each of the Mailscanner
>servers. On the Mailscanner servers we used transport table from mysql.
>
>This is the only good way that we found to do it, I guess you can
>convert this easily two your configuration. Just setup the name server
>to hold primary mailserver as 10 and secondary as 15.
>
>Hope our experience can be to help for you, and if you find another way
>to do it, please tell me.
>
>Best regards
>Egil Fujikawa Nes
>  
>