I’ve been at the receiving end of “undelivered” email notifications with attachments. Asking around, it seems it’ a widespread problem amongst NUS staff.
The campus helpdesk said a spammer sent an email to my email address, and disguised it to appear to originate from my email address (spoof), i.e. from: email@example.com and to firstname.lastname@example.org. Well, the NUS exchange server will redirect spoof emails to junk.
However, these emails contained invalid characters so could not be delivered. Unable to detect the spoof, the server alerts the purported user (i.e. me) so I get spam in the form of undeliverable mail notifications! You can just delete the emails, but the frequency and volume is quite high.
These past couple of weeks, I have been using MS Outlook 2016 to handle NUS emails. It is unable to automatically apply SpamSieve’s AppleScripts to incoming messages. Well, as it turns out, a workaround is now available which I applied.
And so SpamSieve has helpfully relieved me of this plague of “undeliverable” spam.