You must provide at least one recipient email address - but Email IS sent

Hi there

When I (as an author) make a submission, everything works fine, the “Submission Acknowledgement” email is being sent to the author. Still I get an error saying sending of email didn’t work. In the apache error.log I see:

You must provide at least one recipient email address., referer: https://[my-domain]/[my-journal]/submission/wizard/2?submissionId=1256

As I said, the email is still being sent. When OJS sends other emails (e.g. password reset) I also do get the email, but the error does NOT show up in the error.log. So it looks as if it has something to do with the submission workflow.

I am using OJS 3.3.0-13 on Linux. In, it is set up to use an external smtp.

Does anyone have any information or idea on this issue?

Thanks, Matthias