Hello George,
Please increase the log level for SMTP Receiving service to Protocol Communication so we could get more hints of why the message was rejected.
My bet is that the DVR device is using a non authenticated session and, by default, relaying messages to external domains are accepted only from authenticated sessions (otherwise you will be acting as an open-relay, which is not good at all).
If this is the case you have 2 options:
- configure the DVR to send messages with a dedicated account (like dvr@your.domain)
- if this device is a trusted one you may add a relaying exception for that IP address (WebAdmin > Security & Filtering > Acceptance & Routing > Routing basic settings > Allow/Disallow relaying > Exceptions > Add)
HTH,
Ioan