PDF reply

I'm having an issue when trying to reply to encrypted PDFs, the URL looks correct, in the logs I believe this to be the relevant line.

Caused by: java.lang.RuntimeException: Error obtaining injected value for field mitm.djigzo.web.pages.portal.pdf.PDFReply.clientSMTPHost: Symbol 'client.mail.smtp.host' is not defined.

I don't know where that is being read from, or where to set it. Any help would be greatly appreciated.