[K12OSN] Moving our email server

[Jim Kronebusch]

> Thanks Jim,
> 
> You read the question correctly.  I will take a hard look at the config
> files that you mentioned.  Regarding DNS TTL, I may have trouble
> coordinating the changes because I cannot directly update our DNS
> pointers.  I need to have Cox personnel do it.

If you don't have control over things it may be tough to convince an ISP to
reduce the TTL.  You may want to make your change then at lunch or something
and just let users know that the server may be down for a couple hours in the
evening then make your changes at night.  If you can, check the remaining TTL
of the common ISP's in your area.  If ISP 1 expires in 6 hours, ISP 2 expires
in 8 hours, and ISP 3 expires in 4 hours, making your DNS changes 6 hours
ahead of time may cause the least amount of downtime.  I don't have a
recommendation for a good way to check for this any more.  The programs I used
to use were windows based and I don't have a good suggestion for a way to
check this under Linux, but it should be simple (anyone?)

> If I do not need to make any changes to the config files, can you expound
> at all about "a little stupid" regarding the connections to two ISP's?

I left "a little stupid" as vague on purpose.  It seems to me that every time
I have tried such a thing my machines get "a little stupid" when trying to get
to the internet, almost like at times they are not certain which path to take,
but I leave that vague because it still doesn't make sense to me why it
doesn't always work since I only have one gateway.  But if any of your config
files reference eth0 or your external IP, you may not be able to tell them to
listen to eth0 and eth1 and to external IP 1 and 2.  Again it most likely
depends entirely on which programs you are using with postfix and how your
postfix is configured.

I still prefer on late night change overs, getting ahead of DNS, and relying
on mail queue's to prevent lost messages.  Seems the least muddy to me.

I make switches like this quite often, and I have absolutely no problems as
long as I give my config files a good once/twice over for how they listen and
stay ahead of my DNS.  And if I make my change over in the middle of the night
with DNS changing shortly before that, there really isn't many if any messages
being sent at that time of night anyhow.

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