SendEmail ignores the “From” Field
More Fun with Sharepoint and it's excellent (</irony>) Documentation.
Apparently, the SendEmail Workflow Activity ignores the FROM-Property. As per a Comment on the SendEmail.From Page:
This property is currently ignored. The emails it sends are always from the sender specified in the outgoing e-mail settings under SharePoint central administration. Specifying a "From" header in the Headers property also fails.
I can just confirm that, SendEmail.From indeed seems to have no effect, regardless if it's been set through the Binding Property or directly in the Property Page.
Bonus-Link: Completely unrelated to the EMail problem but regardless very helpful to me: An article about creating custom Sharepoint Timer Jobs. Thanks for that one!