So unfortunately despite quite a bit of searching and a couple of unhelpful calls to Optus support (which I am still waiting for a call back from, but that was hours ago and they were going to get back to me within the hour so I'm not holding my breath) I am here to ask the same question so many before me have grappled with. My externally hosted email works spectacularly well on 3G but simply refuses to receive or send when connected to my home optus wifi (interestingly it also does this when I am connected to the wifi at my work which I also believe is supplied by optus). I don't appear to have this issue when connected to other non-optus wifi.
I have done the usual things - rebooted the modem (numerous times), adjusted the incoming and outgoing server settings for the email accout (although why this should need to be changed to suit just my wifi when it works elsewhere is beyond me). Authentication on or off - doesn't matter - still nothing.
So I am hopeful that someone here might be able to shed some light on what appears to be a common problem.
The server settings as supplied are: IMAP Incoming Port 993 SSL, Outgoing Port 465 SSL. Both servers point to mail.caboolturesportsfc.com.au
Hey @BMFC, apologies for the delayed response back to this one.
I've just replied back to your private message. I'm happy to continue chatting with you there.