Re-direct an email domain to another domain for oubound emails in Exchange 2013

In order to re-write the domain for outgoing emails, this can be useful where two companies have merged and there is a new name for the two of them - for example:

user@companyA.com and user@companyB.com now become user@companyC.com

This action can be performed though the Exchange Management Shell using the following cmdlets:

- Get-AddressRewriteEntry: Returns an existing policy.
- New-AddressRewriteEntry: Creates a new policy e.g.

New-AddressRewriteEntry -Name "Address rewrite entry for companyA.com" -InternalAddress companyA.com -ExternalAddress companyC.com

- Set-AddressRewritePolicy: Modifies an existing policy.