Will configuring a backup MX actually do me much good?

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Will configuring a backup MX actually do me much good?

Chris Green-11
I run postfix on an 'always on' machine at home and have the MX record
for my domain pointing at this machine.

Obviously there are occasional downtimes, for example this morning we
had a 3 hour power failure and I also need to upgrade the machine
occasionally.

Now I could of course overcome some of these down times (by using a
UPS etc.) but I have other priorities really so I think things are
likely to stay much as they are at present.

So, if I set up a lower priority backup MX record pointing at a
virtual machine I run on a domain right away from my home machines
would I actually win anything much apart from yet another bit of admin
required?  

Sending systems will automatically back off and retry at intervals (I
have seen this happen when I have upgraded my home server in the past)
so will a secondary/backup MX actually help at all?


Another approach I might take is to have a backup machine here at home
with Postfix configured on it to take over if I know I'm doing an
upgrade on the main machine.  All I would need to do to swap would be
to change the port forwarding destination on my router.  Does anyone
here do something like this and are there any 'gotchas'?

--
Chris Green
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Re: Will configuring a backup MX actually do me much good?

Dominic Raferd


On Thu, 21 Nov 2019 at 12:05, Chris Green <[hidden email]> wrote:
I run postfix on an 'always on' machine at home and have the MX record
for my domain pointing at this machine.

Obviously there are occasional downtimes, for example this morning we
had a 3 hour power failure and I also need to upgrade the machine
occasionally.

Now I could of course overcome some of these down times (by using a
UPS etc.) but I have other priorities really so I think things are
likely to stay much as they are at present.

So, if I set up a lower priority backup MX record pointing at a
virtual machine I run on a domain right away from my home machines
would I actually win anything much apart from yet another bit of admin
required? 

Sending systems will automatically back off and retry at intervals (I
have seen this happen when I have upgraded my home server in the past)
so will a secondary/backup MX actually help at all?


Another approach I might take is to have a backup machine here at home
with Postfix configured on it to take over if I know I'm doing an
upgrade on the main machine.  All I would need to do to swap would be
to change the port forwarding destination on my router.  Does anyone
here do something like this and are there any 'gotchas'?

I use a VM in a different country with the same priority MX so that we should have effectively zero overall downtime. (The exceptions are when I propagate a broken configuration from one MTA to the other - oops.) There are some complications to this setup but I have it working neatly. However I have often heard it said here that such an approach is overkill.

It is true that occasional downtimes may not be a big issue for incoming emails - they should be deferred and then resent by their MTAs when your MTA is back online. But if you (+others) need your MTA to send outgoing emails it may cause aggravation when it is down, especially as MUAs do not necessarily (or ever?) wait and retry.
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Re: Will configuring a backup MX actually do me much good?

Gregory Heytings
In reply to this post by Chris Green-11

>
> Sending systems will automatically back off and retry at intervals (I
> have seen this happen when I have upgraded my home server in the past)
> so will a secondary/backup MX actually help at all?
>

It's up to you to decide what your priorities are.  It's true that sending
systems automatically retry delivering emails, but this means at least (1)
that you experience delivery delays when your main MX is down, (2) that if
your main MX is down for a long period (e.g. you're on vacation and cannot
reboot, your internet connection is physically down and needs to be
repaired, ...), and (3) some sending systems (typically mailing lists)
maintain a record of delivery failures and will stop trying to send emails
for you when there are too many failures.  In cases (2) and (3) you might
lose emails.

Gregory
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Re: Will configuring a backup MX actually do me much good?

Chris Green-11
In reply to this post by Dominic Raferd
On Thu, Nov 21, 2019 at 01:00:24PM +0000, Dominic Raferd wrote:
>    I use a VM in a different country with the same priority MX so that we
>    should have effectively zero overall downtime. (The exceptions are when
>    I propagate a broken configuration from one MTA to the other - oops.)
>    There are some complications to this setup but I have it working
>    neatly. However I have often heard it said here that such an approach
>    is overkill.

My VM is also overseas (from me)! :-)  How do you read mail then that
may get delivered to either of two places?


>    It is true that occasional downtimes may not be a big issue for
>    incoming emails - they should be deferred and then resent by their MTAs
>    when your MTA is back online. But if you (+others) need your MTA to
>    send outgoing emails it may cause aggravation when it is down,
>    especially as MUAs do not necessarily (or ever?) wait and retry.
>
Not really an issue for me, I'm the only user of the local postfix and
I can send mail from elsewhere if I get desperate.

--
Chris Green
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Re: Will configuring a backup MX actually do me much good?

Chris Green-11
In reply to this post by Gregory Heytings
On Thu, Nov 21, 2019 at 01:04:45PM +0000, Gregory Heytings wrote:

>
> >
> > Sending systems will automatically back off and retry at intervals (I
> > have seen this happen when I have upgraded my home server in the past)
> > so will a secondary/backup MX actually help at all?
> >
>
> It's up to you to decide what your priorities are.  It's true that sending
> systems automatically retry delivering emails, but this means at least (1)
> that you experience delivery delays when your main MX is down, (2) that if
> your main MX is down for a long period (e.g. you're on vacation and cannot
> reboot, your internet connection is physically down and needs to be
> repaired, ...), and (3) some sending systems (typically mailing lists)
> maintain a record of delivery failures and will stop trying to send emails
> for you when there are too many failures.  In cases (2) and (3) you might
> lose emails.
>
Yes, you're right, I did get dropped off a couple of mailing lists the
last time I was off air for a long time.  

Rebbooting isn't a problem, there is always someone who can restart
the system for me, though I suppose if there was a hardware fault I'd
be a bit stuck.

So what do others do?

    Have an off-site secondary/backup MX and a means of getting mail
    from that system.  That's my issue with this approach, I mean I
    could *read* the mail but it won't get delivered into my filter
    system at home and thus to the right destination directories etc.

    Have a local backup system to switch to when main system is down.
    Probably a bit easier to manage and if it is synchronised with the
    main system then filters etc. can still work.

    Do what I did until recently and deliver all mail, unfiltered, to
    an off-site system using my hosting service's mail forwarding.
    I can at least ready all my E-Mail there.  I actually turned this
    off recently because I so rarely needed it, maybe I should turn it
    back on.

    Anything else?

Thanks for the feedback so far, all useful stuff.

--
Chris Green
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Re: Will configuring a backup MX actually do me much good?

Dominic Raferd
In reply to this post by Chris Green-11


On Thu, 21 Nov 2019 at 14:53, Chris Green <[hidden email]> wrote:
On Thu, Nov 21, 2019 at 01:00:24PM +0000, Dominic Raferd wrote:
>    I use a VM in a different country with the same priority MX so that we
>    should have effectively zero overall downtime. (The exceptions are when
>    I propagate a broken configuration from one MTA to the other - oops.)
>    There are some complications to this setup but I have it working
>    neatly. However I have often heard it said here that such an approach
>    is overkill.

My VM is also overseas (from me)! :-)  How do you read mail then that
may get delivered to either of two places?

The mailservers relay emails into Gmail. They also quarantine some emails - these are passed on to the 'primary' mailserver (when it is available) to be reviewed for release/removal.