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I want all mail to go to two SMTP servers and each server does everything it would do if there was only one SMTP in the first place.

In other words people get mail in two places and they are out of sync.

The scenario is we have Google Apps AND a custom app that uses parse incoming email. The problem being solved is the app is not 100% reliable and as such we need All incoming email to go to both places.

I have no idea what I should be looking up as the above goes against all common sense and standard IT practises....

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Your question isn't very clear... do you mean you want all incoming email to go to two places (Google Apps and your custom app)? – Ward Oct 2 '11 at 4:10
it says "as such we need All incoming email to go to both places." this to me means i want all email to go to both places, as in one place is Google Apps and the other place is sendgrid - how should I say this so it is clear? I also said "I want all mail to go to two SMTP servers" - this again to me means, I want all email delivered to 2 places. how do i say this clearer than what I have already said? – SoreGums Oct 2 '11 at 12:32

A foreign SMTP server will always have only one conversation to transfer your email. If you want your email sent to two servers, you need to have a receiving server that is configured it forward it to the other systems, or configure one system to forward to the other while storing.

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I can't configure Google Apps or sendgrid servers... Are you saying postfix etc are only capable of of 1 to 1 mappings? And then are you saying I have to write my SMTP server to deliver to two separate SMTP servers? The thanks – SoreGums Oct 2 '11 at 3:07
Your own postfix server can deliver to both. If you point your MX record at it, then that will work. You just can't somebody else's server that isn't under your control to send it to two places for you using MX records. – Jeff Ferland Oct 2 '11 at 3:52
ok so do you know what I should specifically be looking up in postfix or any smtp software to do what I want to do? – SoreGums Oct 2 '11 at 12:31
It can be done with Postfix and some fancy work involving filters. It may be possible to do with Postfix directly through some configuration wizardry. I can't tell you what will work without setting up my own dummy network to figure it out, and that won't happen until at least the weekend. – Jeff Ferland Oct 4 '11 at 4:43

However, if you only need to do this for few addresses within the domain, you could handle this with an alias for the relevant addresses which expands to two different unique addresses.

If you are doing this for all the addresses in a domain you could consider a wildcard alias.

Exim will allow you to have a transport which delivers email, but does not do the final delivery. For the addresses that need to be handled by the sendgrind servers, it could deliver to them. Then normal delivery could be used to process delivery to Google apps. I would expect other servers to have similar capability.

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