Question

How would you set a forwarder to forward all emails received to 1 external address?

Exchange Server, Email, DNS

How would you set a forwarder to forward all emails received to 1 external address?

Here is the situation:

We have a client that is hosting their own email on their Exchange server with pop accounts outside of the HQ building. We will be hosting their mail on our servers under the same domain name. Their MX record is pointing to mail.domain.com and mail.domain.com is pointing to their exchange server. We will be changing the "A" record of mail.domain.com to our server so all mail will be redirected to our server instead of theirs. This company is global so there will be lag times involved with getting all of the DNS servers resolving to the new server IP for mail.domain.com. During this time, some mail will be delivered to the exchange server and some will be delivered to our server. We need a way to either forward all of the mail received by the Exchange server to an external address or just to be able to view complete messages received during this time by the Exchange server. If I remember correctly, the Exchange admin can view all messages in any account on the exchange server but I forgot how. Would it be easier to forward if that is possible?

A couple of things to consider is that changing the A record is a start. I would suggest also changing the lifetime on the record to a shorter timeframe. This way the record will expire quickly and changes will propagate faster.

I would also recommend putting another MX record in with the weight or priority set lower on the record pointing to your organization's mailserver. This will ensure that messages are delivered through your server(s) before hitting theirs. By adding another MX record pointing to your Exchange servers, you can shut theirs down from accepting inbound requests on port 25 and all messages will be stored on your server then for the customer.

MX records do not have to match the customer's domain. For example:

customer.domain.com IN MX 100 server.hosting.domain.com
customer.domain.com IN MX 200 server.customer.domain.com

Where server.x.domain.com is an existing A record.

Since the first record is lower priority, inbound servers will attempt connecting to this host first. If the first server does not respond, then connections are attempted to the second host. If the host is not available, the sender's system may retry for some set period or send back a non-deliverable notice to the original sender.