> What do other people with perm connection who run their own mail
> server do for secondary/backup?  (ie. secondary mx)

My suggestion is that you *DON'T*!

Why not you ask? Think about how the mail system works. Someone sends
a mail to you, it goes from their desktop/mail client of choice onto
the mail queue of their outbound smtp server. The server then does an
MX lookup of the domain and get's your mail servers IP. If it can't 
establish a connection to your machine it will then queue the mail and
retry every hour for up to four days. (this is dependant on the mail
system config obviously but that's the recommended standard). If your 
mail system is still not up then the sender gets a bounce saying you
didn't get their mail.

If however you have a secondary MX then the smtp server, when it can't
contact your box will send it there. And that server does what with the
mail?......Precisely the behaviour of the originating server we just 
described. I.E the secondary adds what value? NONE in fact it is worse
than that, consider if the secondary server goes down while your mail is
queued up on it, no mail system at $11/month is gonna have transaction 
logging on it so when they recover it, it will be from last nights backup
so all the mail received and queued today for your server will be lost. 
That's *ALL* the mail queued up to your domain from anywhere in the world
not just from our example sender. This means that the recipent has no 
idea that they are missing mail and the sender gets no bounce back to say 
that the mail wasn't delivered. However if you don't have a secondary then
mail for your domain will be queued up on a whole bunch of outbound smtp
servers around the world. If our senders local outbound smtp was to suffer
a crash and be rebuilt, only mail from that part of the world would be 
missing as mail from other domains will be queued up on their still 
functioning servers, and most erstwhile system operators would tell their
users that the outbound server crashed and any mail they sent in the last 
couple of days should be re-sent. But your secondary MX would have no idea
who's mail could be queued up on it cause it could have come from anywhere
in the world so they won't be able to tell them even if they had the desire
to do so.

If the secondary queues the mail for longer (so that you can get your machine
back together before messages start bouncing) then that is not necessarily
better, How long should someone wait before the system tells them that you 
didn't get the message. Mail that goes stale is worse than mail that get's 
bounced. Fair better for the sender to be told you didn't get the mail so 
that they can ring you and invite you to the pub, instead of just assuming 
that you got the message but are under the thumb so won't come for a beer.

Ok enough of a rant but you get the picture, $11 / month is not value at all
their charging you money for a service you would be better off without.

HTH

Pete





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