Author: W B Hacker Date: To: exim users Subject: Re: [exim] Linux-HA / Routing according to IP address received upon
James Davis wrote:
> Matthew Newton wrote:
>
>
>>Set up two hosts, on two IP addresses, with the same MX number?
>>
>>Seems the most obvious to me. We have three mail hubs like this;
>>occasionally SpamAssassin will fail on one, but the others keep
>>processing just fine. That's the nice thing about SMTP; it's
>>resilient by design ;-)
>
>
> At the moment I'm running an IMAP server directly on the MX hosts,
> failing that over between the two. I want to make sure that the mail
> ends up on the host with the active IMAP server - hence the rerouting to
> the shared IP address. I'm thinking perhaps it would just be easier to
> run the IMAP server elsewhere :-)
>
> James
>
>
>
You've hit the right nail on that one.
- because of retry, and/or multiple mx, a failed MTA doesn't
have to be fixed in 'seconds', though minutes rather than days
is nice.
- but a POP or IMAP that doesn't respond to 60-second,
5-minutes, etc, checks for mail has users reaching for the phone.
- likewise the 'submission' side of an MX, Unlike a 'peer' MX,
it is a rare luser's MUA that can 'fall back' to a secondary MSA
for sending. Once again - a failure to (be able to) send gives
rise to calls for help in minutes, not hours.
IMAP (including most Webmail) is particularly demanding of
storage congruency - else more calls 'where has my ...
folder/contents gone?' calls.
No 'one size fits all' solution, but RAID, external, and
'hardware' shared, not nfs, then 'standby' MTA / MSA and
POP/IMAP with an external IP-takeover 'watchdog' might at least
keep it to a two-box or three-box solution.
Keeping luser's mailstore in sync is IMNSHO, the biggest challenge.
