CRM 4.0 Email router

On Exchange Server run the process "Microsoft CRM Email Router" under CRM administrator account.

CRM external connection configuration

Basically, in my case it was upgrade form CRM3.0 to CRM 4.0. To configure external access (not from your local network) you need to use Microsoft tool - http://support.microsoft.com/kb/948779 - Microsoft article with description and links to download. One thing I want to clarify- if client IP address is not belongs to list of local networks what you specify in "IFD Internal Address and Subnet Mask" - the tool does redirection to form authentication dialog instead NTLM authentication if client IP address in IFD internal network subnets range.

CRM 3.0 Undeliverable mail

Description: In crmmail mail box on exchange server thousands mails in undeliverable folder and tens mail in inbox. In application event log on exchange server multiple error messages from MSCRMExRouterService the error begins like this:
Microsoft.Crm.Tools.ExchangeConnectorService.ExchangeSinkServiceException: Verifying before delivery message: CRM - Account Hierarchies in mailbox: CRMmail failed (System.Net.WebException: The request failed with HTTP status 401: Unauthorized.
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Fix: change logon account for CRM router service from system local to account for CRMMAIL mail box, enter CRMMAIL account as member of PrivUserGroup.
According to Microsoft CRMMAIL mail box should be empty at all time. The messages should be evaluated and deleted immediately upon receiving.