While working on a MOSS 2007 to SharePoint Server 2010 upgrade recently I ran into a unique requirement involving the domain suffix used for inbound emails. Since this particular upgrade was also a consolidation of multiple SharePoint farms I found myself in a situation where I needed SharePoint to accept email on multiple domain suffixes. Since this is a farm wide setting I had a feeling that the secret would lie in the local SMTP configuration but I was unable to find confirmation.
Old SharePoint farm domain suffix = @oldserver.SharePoint.local
New SharePoint farm domain suffix = @newserver.SharePoint.net
Setting up inbound email in SharePoint is well documented, as is configuring the exchange connectors needed to relay mail to the local SMTP service running on the SharePoint server. So there is no reason to document configuring SharePoint to accept mail on the new domain suffix initially.
Only two additional configuration changes were required. The first was a second exchange connector the was configured to also forward any mail addressed to @oldserver.SharePoint.local to the SMTP service running on the SharePoint server. The second was to create a domain alias on the SharePoint server for @oldserver.SharePoint.local.
Start -> Administrative Tools -> Internet Information Services (IIS) 6.0 Manager
Expand the SMTP Virtual Server that you created when you set up the primary suffix.
Right click on “Domains” and select “New -> Domain”.
And that is all there is to it.