Re: [exim] Is a secondary MX worth the effort?

Ken Price wrote:
>> One of the things I've considered for #2 is having a secondary MX
>> which is configured to give back a 4xx for everything.
>> However, I don't know if there are sending hosts who would fail to
>> go back to the primary MX when it came back up.
>>
>
> This is an interesting idea and I feel like an idiot for not thinking
> of it myself - course that's why we have these lists :-) Does anyone
> know how effective this method may be? I like it because of it's
> simplicity, low/no maintenance, and ridiculously low system
> requirements. I could have one or more $15/month VPS servers running
> in this role.
>
> However, the question remains, is this method more effective than
> leaving it up to the sending MTA to retry a connection failure?
>

I don't see any point in having a secondary MX only answering by 4xx
messages. This will only give you problems. As Mark Perkel noticed quite
some time ago, if qmail receives a 4xx error, it only retries on the
same MX, so all mails sent to the 4xx backup by qmail will be lost.
Also, an unreachable MX should give you the same sender retry rate than
a 4xx backup.
In short, this is useless and will give you troubles, nothing more. If
you need a second MX, it should be properly configured with the same
kind of virus/spam scanning than the first one.