Microsoft CRM "du jour"

If you are implementing a CRM Online solution, you need to take into account wich emails scenarii you want to handle.
The email flows are exactly the same as the On Premise version, but the CRM Online does not contains an e-mail router service implementation.
Basically, there's no outbound (ie:smtp, exchange)  or inbound (ie: exchange, pop3,..) email service hosted in the cloud.
Here's the two aspects of the implementation

No implementation of the e-mail router service
Your only option is to use the e-mail router embedded within the outlook client.
Outlook will send and receive emails the normal way and; following your crm options, inboud or outbound emails will be tracked into MSCRM Online.

The drawback is that only emails send/received with a CRM User linked to an Outlook client will be processed.
So, let's say you have a workflow sending an email in response to a certain condition, that email will ONLY be sent if the following conditions are met :

• The sender has outlook with a MSCRM add-in installed
• The sender is configured in MSCRM User Settings with an E-mail access type Outgoing of type "Microsoft Dynamics CRM for Outlook"
• The sender's outlook is connected (both to MSCRM and the smtp).

In short, while not impossible, as you could always dedicate outlook clients as email routers, it is very difficult to manage emails from/to queue or for users not always connected.
All emails not going to an outlook instance will stays flagged as 'Pending Sent' in CRM Online. ('Pending E-mail Sent' Prompt)

Implementation of an e-mail router service
The email router installs and works as if you run an On Premise installation; the only difference being the connectivity from the e-mail router is not local but goes to the internet to make the web service calls to the CRM Online.
- Outbound emails will be read by your e-mail router and routed trough your smtp (exchange or plain smtp)
- Inbound emails will be read from your POP3, Exchange or Live accounts and send via the e-mail router to CRM Online.
You keep the option for each User or Queue to specify which method is used for email connectivity inbound and outbound : None, E-mail router or Outlook Email Router.

For more information about installation of the e-mail router service to a CRM Online installation,
see this document for CRM 2011 online: http://www.microsoft.com/downloads/en/details.aspx?FamilyID=ec184209-991c-4cd6-a127-bf14cbc4094b 
or this document for CRM 4.0 online : http://www.microsoft.com/downloads/en/details.aspx?FamilyID=6949F8E3-282E-43F9-91E7-2E647880D3C1