I have a new external site in 2013 configured with FBA. On a list, I have a Designer workflow that does the following:
Email an address directly
Email a FBA account (that has an email address affiliated with it)
Email the "Created By" user for the item
1 succeeds, while 2 and 3 fail and both log in the history: "The e-mail message cannot be sent. Make sure the outgoing e-mail settings for the server are configured correctly."
Out-going email settings are set in Central Admin, and another external site configured with FBA on the same farm has no problem with any of these emailing examples. What could be improperly set on the new site that's stopping certain emails (with the only connection being to FBA accounts) from going through?