LifeinAsia - 3:49 pm on Aug 17, 2010 (gmt 0)
I've seen that too a few times.
Are order receipts, account creation notifications, and responses from the contact us form all coming from the same e-mail address? (I've seen cases where firstname.lastname@example.org might be blocked, but email@example.com isn't.)
What if them made a typo, but it's not bouncing? For example, they are firstname.lastname@example.org, but they fat fingered it as email@example.com, which also happens to be a valid e-mail account there.
Another possibility is that they simply accidentally deleted the e-mail and didn't remember deleting it (maybe they had a bunch of spam messages delivered around the same time).
Oh, and I've seen cases where the message was delivered to their server, their server's spam trap ate it, but apparently it didn't digest well because future messages went through fine. (The sysops could have been tweaking their filters when the first message tried to go through.)