UPDATE: Madjur Ahuja points out this link from a newsgroup discussion: http://msdn2.microsoft.com/en-us/library/ms772417.aspx. It’s pretty definitive.
We often want to embed hyperlinks to InfoPath forms in emails sent from SharePoint Designer workflows. When users receive these emails, they can click on the link from the email and go directly to the InfoPath form.
This monster URL construction works for me:
Replace the bolded red text with the name of the form, as shown in the following screenshot:
Note that there is a lot of hard-coded path in that URL, as well as a URL-encoded component. If this is too hard to translate to your specific situation, try turning on alerts for the form library. Post a form and when you get the email, view the source of the email and you’ll see everything you need to include.
Astute readers may notice that the above email body also shows a link that directly accesses the task via a filtered view. I plan to explain that in greater detail in a future post.