Re: [SLUG] Secondary Mail Server

[Peter Rundle <peter@xxxxxxxxxxxxxxxxxx>]

Dean Hamstead wrote:
[snip]
> Keep in mind that if your primary mail server is down, other mail 
> servers wanting to deliver will hold on to the mails and retry for days. 
> So a secondary is not strictly necessary.
[snip]

I would even go further than Dean and say that adding a secondary to "hold the mail" whilst the primary recovers, is not helping 
and is in fact making the problem worse. As Dean said, if you don't have a secondary, in-bound mail to your domain is safely held 
in the outbound queues of the multiple servers who's users have tried to contact your users.

The recommended behaviour, (iirc), is to try to connect to your server once an hour for up to four days. If the mail cannot be 
delivered after this time, the email is "returned to sender" saying that the mail was not delivered. So you basically have up to 
four days to get your server back together and you won't loose any email. And if it takes you longer than four days, the users who 
sent the message at the very least know that the email didn't make it and can resort to alternate forms of communication to 
contact the intended recipient.

However, if you set up your mates server as a secondary and it works fine, what value has it added over holding the mail on the 
original senders outbound smtp? But if your mates server was to also die say two days after yours, then guess what, all mail for 
those two days is totally goneski! The sending servers might have a record in their log files that they sent the mail to your 
mates server, but they won't have a copy. The original sender probably has a copy in their outbox, but they think that the email 
was successfully sent and they will never get a notification that the mail could not be delivered to it's final destination. You 
don't have it and, unless you backed up your mates server every time an email arrived, you don't even know who sent you emails for 
that period so as to be able to contact them and ask them to resend. Furthermore, if it takes you more than four days to get you 
primary back on-line, the users sending emails into your domain are never notified that their email is not being delivered to the 
recipient but is sitting in a mile long backlog on your mates server. So they are wondering why, after a week, the recipient 
hasn't responded.

How is this better than no secondary?

There are good reasons for setting up a secondary, but "holding all emails in case the primary is not on-line" is not one of them.

If however you are doing it for the intellectual exercise, that's a different story. :-)



HTH

Pete