I have an on-premise software and on-premise exchange 2013 server. The software requires IIS SMTP to handle the email from/for clients (Helpdesk software). I have the proper Relay established on the exchange server. Anything sent to domains OUTSIDE the local domain works fine. However, when the iis smtp sends an internal email to one of us, it goes into delay and dies after a day. In the relay security settings, I have TLS, Externally Secured on authentication and on Permissions, I have Exchange servers and anonymous selected.
The helpdesk software is using IMAP. I have successfully tested on port 143 and 993 for SSL.
On my DNS, I have the MX set to my mail.domain.com and a valid Reverse defined.
Everything works EXCEPT local email delivery. From testing, I'm certain it is something I've misconfigured on the IIS SMTP side. Exchange is good. OWA is good, everything.
Kinda at a loss.