One bit of advice: To get more responses to this question, add it to the Microsoft Dynamics Zone - you'll get some more Microsoft CRM folks in that group.
Most CRM solutions offer some direct integration with various different email campaign services (for example, Microsoft CRM can integrate with solutions from Exact Target and c360). The integration is usually "good" but not "great" (in other words, the integration may or may not create campaigns for you in your CRM tool - and click-throughs almost never create campaign responses in CRM ... you'll usually have to track those directly in your email tool).
So it really depends on what you want to accomplish.
(1) CRM: If you have a lot of goals for a CRM tool (improving your sales pipeline management; providing a better view of customer data to sales, service and marketing; automating customer service; tracking all your campaigns - not just email - in one tool; etc, etc), then you should get a CRM tool.
(2) EMAIL: If you do a nominal amount of email marketing, then you might find that the email capabilities build directly into your CRM tool are sufficient for your needs. But if you do a lot of email marketing (i.e. more than 1000 emails sent monthly), then you will certainly want to look into using a third party email tool (usually hosted is a better solution in this case).
(3) INTEGRATION: If you need both a CRM tool and an EMAIL tool, then why not look for a combination that integrates well with each other? This will improve your trackability in addition to (most likely) making you a more efficient email marketer.
(4) HOW TO INTEGRATE? If you decide that it is a good investment to have both tools - then you need to decide:
* Do you need "best of breed" for both tools - in which case you may end up having to do the integration on your own
* Or, will you look for a tool that has some built-in integration options?
Every good CRM and EMAIL tool on the market today offers an API. So if you've selected good tools, then writing your own integration should certainly be an option. However, all except for the largest businesses with large budgets should probably look for a cost-effective integration solution.
Back to your example of Microsoft CRM - you should probably look into what c360 and Exact Target offer if you want to have an integrated solution. We're also big fans of Vertical Response and Constant Contact - although neither of those email marketing solutions have integration options for Microsoft CRM yet.
