Migrating to new machine and dealing with mail and dns lag

[cmdln]

I am preparing to migrate to a new machine. I've been burned in the past with DNS. Setting the ttl low ahead of time helps but it only helps so much. With websites when I move I setup a reverse proxy on the old machine and configure it to proxy to the new machine. How can I allow exim to relay mail for a domain but not deliver it locally?

I see

domainlist local_domains = lsearch;/etc/localdomains

domainlist relay_domains = lsearch;/etc/localdomains : \
    lsearch;/etc/secondarymx

in /etc/exim.conf
Should I just comment the domain out of /etc/localdomains and add it to /etc/secondarymx?

I know if I just disable mail for the domain it will eventually arrive but customers should not have to wait days for a response if it can be avoided.

[nickp666]

You could for ease just forward all designated mail to the other server, a router for exim would suffice here (although it may cause some backscatter)

send_to_gateway:
     driver = manualroute
     transport = remote_smtp
     route_list = * your.newserver.com

Or as a second option without the backscatter, you could set up a static route driver and run verifies to check the end recipients exist on the new machine (more manual config needed in this case though)