I have a Workflow (created in SPD 2013) that sends Emails, either directly or through a Approvaltask. The problem is that none of these Emails reach their destination. They don't even reach the Mailserver. The SendMail Command works fine in code, powershell and also in 2010 Workflows (= I actually receive the mail). The Mailserver is in the same domain.
After a lot of research I found out, that the Workflow Engine in 2013 sends Emails anonymously but I already checked and the Emailserver should allow them. Then I thought it might have something to do with the problem that some users do not have a Email assigned as seen in the People Picker. Configuring the Profile Syncronization did set Mails on every user from the Active Directory but the problem was the same.
The Workflow UI of the associated ListItem shows me a 400 Bad Request as soon as the Workflow reaches a Send Mail Command. The only "useful" information from the corresponding SP Logs show
Couldn't find a user using property 'WorkEmail' of value 'loginname@domain'. The Email displayed shows the loginname of the user that started the Workflow but it isn't even correct as the users mailaddress is quite different.
What is the problem here? After working a whole week on it, I don't really know what I still could do to resolve this issue.