I'm used to receiving spam emails about "urgent" security issues from "banks", some of which I have an account with, and others that I don't. They go automatically to "junk". But the email in my inbox seemed to be from Optus, and I nearly fell for it! It was headed "Valued Customer", and the text was ---
Your mailbox has exceeded 90% of its quota. When it reaches 100%, new messages will be rejected and bounce back to the sender. To avoid missing mail, please keep your mailbox at a reasonable size. Refer to....[then a link to what appeared to be an Optus FAQ site was set out].
Yeah, I thought, it's just possible my settings in Thunderbird don't provide for automatic deletion of old emails. And I was on the verge of clicking...but....."Valued Customer"? Would Optus use that? So I checked the settings in Thunderbird (they provided for automatic deletion), and then checked my mailbox on-line (not clogged up with old mail). Thus, the email was obviously spam, and who knows what would have been the result if I had allowed my account to be hijacked (which I assume was the objective).
Just goes to show, it's important to be on your guard. There's always a new angle that might catch you unaware.