Create Shadow Redundancy Cross Forest in Exchange 2010

Send connector cross forest shadow redundancy

New-SendConnector ToTailspin -AddressSpaces SMTP:tailspin.com -SmartHosts mail.tailspin.com -ProtocolLoggingLevel verbose -DNSRoutingEnabled $False -SmartHostAuthMechanism ExternalAuthoritative
Get-SendConnector ToTailspin | Add-ADPermission -user "MS Exchange\Externally Secured Servers" -ExtendedRights ms-Exch-SMTP-Send-XShadow

Receive connector cross forest shadow redundancy

New-ReceiveConnector FromFabrikam -RemoteIPRanges 192.168.100.1 -Bindings 0.0.0.0:25 -ProtocolLoggingLevel verbose -Banner "220 Tailspin XShadow SMTP Server" -AuthMechanism ExternalAuthoritative 
Get-ReceiveConnector FromFabrikam | Add-ADPermission -user "MS Exchange\Externally Secured Servers" -ExtendedRights ms-Exch-SMTP-Accept-XShadow