CMGW is Connection Manager Gateway.? I'd guess that there was a problem with GIO making a connection via the manager to secureserver.? The GIO site will keep trying to send emails until it's either successful or gets a bounce reply.
I think CMGW must be a part of Nick's setup, not a part of Groups.io. Hence it still sounds like greylisting to me.
That is, it probably wasn't so much a problem making a connection as being given a 4xx "try again later" response from CMGW. Finally (five hours later) CMGW gave a 2xx "success" response and passed the message on to the rest of Nick's inbound chain.
In the screenshot, rows 0, 1, and 2 would be the inbound leg from Nick to Groups.io, 3, 4, 5, 6, and 7 would be the outbound leg from Groups.io to Nick's email interface.
Shal
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