I'm stuck with satellite NBN in my country house so I'm using SkyMesh. I'm having trouble sending Optus emails even though SkyMesh doesn't block Optus domain names. The Apple Mail connection doctor reports no problems and I can receive mail and send with IMAP accounts. Do I need to change the settings to send SMTP from outside the Optus network?
You can try using authentication as I did in the last post on the link below or try using SkyMesh outgoing mail servers. I'm not sure of the status with Optus imap so you might have to use authentication with a pop account no ssl, port 25 with Optus.
Edit: I also noticed a recent post from Dan that might help with imap and ssl ports.