Christophe asked a question about how to allow anonymous users to start workflows in SharePoint 2010. The question spread on both Twitter and SharePointOverflow before I had a chance to answer directly, so I’m posting the response here rather than trying to chase all the locations
By default, anonymous access to run declarative workflows are disabled. This only affects anonymous users because a workflow started by an anonymous user would need to be assigned special credentials that would exceed the normal permissions of the anonymous user. For authenticated users, the workflows run with the credentials of that user, but there are no such credentials for anonymous users.
This situation occurs when you’re trying to email enable lists that have automatically launched workflows attached. In these scenarios, anonymous users can send emails to a list and have a workflow start, regardless of their permissions on the list.
It’s actually a very useful feature, and I’ve described such a scenario as part of a solution in an article I wrote several years ago on SharePoint Designer Workflows. Back then, anonymous access was enabled by default. In WSS3 SP1, Microsoft changed the behavior to not allow anonymous access at all, but allowed it if you set a special property in WSS SP2.
You can enable anonymous workflow access by setting the declarativeworkflowautostartonemailenabled property on the farm, either using SharePoint Manager 2010 or through PowerShell or STSADM:
stsadm -o setproperty -pn declarativeworkflowautostartonemailenabled -pv true
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