On SharePoint 2007, I enabled a document library to receive emails. I then use a workflow to send a response to the user who sent the message. The workflow uses the field "Created By" whose value is usually the sender.
About 40% of the time, however, "Created By" is set to "System Account". I was not able to understand why this happens. There does not seem to be any difference between the users for whom it works and those for whom it doesn't. For example, I can find them in the people picker using their email addresses.
Do you guys have any idea why this happens? I am also interested in alternative solutions to send an email back to the sender.