I'm no novice to email.
Let me preface this with I used to build an email product in the early '90s for Lotus, I'm very familiar with email gateways and such, fairly well versed on the latest email technology too, so for me to post this means I'm severely stumped.
Here's the situation, I send out auto-response emails to member actions on my server that seem to vaporize every now and then for no reason.
Not too frequently, maybe a handful every month, but just enough emails have trouble being vaporized to lend credibility issues to my service with new customers.
My site isn't in any DNSBL, I have SPF enabled, and I warn people in big bold red letters to "CHECK YOUR SPAM FOLDER".
My email servers are very efficient, delivery is typically less than a couple of seconds from the order being placed or account registration to delivery in their inbox.
However, with everything running top notch and squeaky clean, every now and then I get contacted by someone claiming they didn't get their order receipt or account creation notification.
I check the email queue and it's always empty, they all clear, unless someone makes a typo and it's bouncing.
Customers always claim they checked the spam folder like I suggested and it's simply not there.
Doesn't seem to be anything in common when this happens either, like a common host or anything like that.
Here's the other odd thing, once they contact us directly via our "contact us" form and we email them directly, %99.9999 of the customers seem to get our direct emails.
Anyone have any possible ideas as this problem is driving me nuts!