Hi Bob. Indeed, creating an exception to the transparent proxy and a DNAT rule is the workaround I've ended up with. This is not very satisfying to me, though, as there are multiple mail-sending services on that remote server, and only one of them is having this annoyance. Yet the exception must be made for the entire server. Are you quite sure that the DNAT intercepts traffic *before* the transparent proxy? Because in my testing it does not appear to work this way. Before moving to the SMTP proxy, I had a DNAT rule in place to handle incoming Exchange mail delivery. But once I turned on the transparent proxy (and without disabling the DNAT rule), the SMTP proxy log was abuzz with activity. I have seen you several times in the forums here recommend avoiding using transparent SMTP proxying, but I'm not clear on your reasons for this. In our case it appears to work just fine. Furthermore, if there are any problems there I can simply switch it off and let the DNAT rule take over. I'd like to know if I'm missing something here...
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