You can try this method:

- Mark new external server as BACKUP MX in your DNS.
- Mark new internal server as PRIMARY MX in your DNS.
- [OPTIONAL BUT RECOMMEND] Sync mail accounts which stored in LDAP/MySQL between BACKUP MX & PRIMARY MX, so that BACKUP MX won't receive spam mails which sent to non-exist users.

BACKUP MX server will push all mails to PRIMARY MX when it's online.

Warning: It seems not all mail servers will contact BACKUP MX to send mails - although most of all will do it.

thanks for the suggestion; I was also looking at some postfix guides for primary/backup MX.
The problem in my case is that internet connection to the internal server is very poor; if I set it as primary MX, the incoming mails (and spams) will cause bottleneck for the whole internal network.

Is it possible to fetch all mails from the external server using a single account?

thanks,
Tony

And, would you mind share us you iRedMail story in our Success Stories forum?

done. I also plan to write a short doc describing steps I did to get IRM working with external LDAP (gosa in my case).

- Mark new external server as BACKUP MX in your DNS.
- Mark new internal server as PRIMARY MX in your DNS.
- [OPTIONAL BUT RECOMMEND] Sync mail accounts which stored in LDAP/MySQL between BACKUP MX & PRIMARY MX, so that BACKUP MX won't receive spam mails which sent to non-exist users.

BACKUP MX server will push all mails to PRIMARY MX when it's online.

Warning: It seems not all mail servers will contact BACKUP MX to send mails - although most of all will do it.

I have installed IRM (with an external LDAP server running GOsa, 1 domain only, let's call it example.com) and all works together very nicely. Now I am trying to do this: install 2 instances of IRM (referring to the same ldap server) as follows:

- one is external, has good connection to Internet and is always online. This servers as the primary MX for domain example.com

- one is placed inside the internal network, has slow connection to Internet and is switched on/off on a daily basis. This serves as the internal mail server.

- each user has email address in form abc@example.com

- mails from Internet sent to @example.com are accepted and stored on the external server

- when the internal mail server is on, it keeps pulling mails from the external server, so that mails sent to @example.com are delivered to the internal mail server.

Can someone please suggest  (very roughly) how to achieve the above?

I think one possible method is to use fetchmail or getmail to fetch mails let's say each 10min from the external server. But I could not figure out how to fetch all new mails for all users via a single account.

thanks,
Tony