We're in the process of moving some services to our new datacentre in Amsterdam. I've just pointed our secondary MX and nameserver there, which means that the IP addresses of
in2-smtp.messagingengine.com have changed.
The new addresses will propagate over the next 24 hours, after which time the old servers in Iceland will be shut down.
Unless you've hard-coded the old addresses somewhere, you shouldn't see any difference.