I have a Visual Studio 2010 workflow for a SharePoint 2010 Server. It uses the default workflow action "SendEmail" to send an e-mail. Everything works out perfectly, but the sender of the e-mail is not the address I set in the "From" property of the "SendEmail" action ...
The From address of emails sent from workflow is fixed to the address set in Central Administration and can not be changed.
The following options are not supported by the current version of the Send an Email action:
Specifying an address on the From line. E-mail messages sent by the workflow always show the e-mail address specified by the server administrator on the From line. Only the server administrator can change this, and it can only be changed for all notifications in the current Web application, not per workflow.
There is a project on Codeplex (spdactivities > Send Email Extended) that allows you to do this.
Alternatively you can send mail using .net's system.net.mail without these restrictions
Is the sender of the email the 'From' address you specified in the Outgoing Email Settings in SharePoint? This should work - I have used the SendEmail action quite a few times with no issues.