I've been using the Mandrill service to deliver automated emails from my web site (using their php APIs.) The service seems to work, except sometimes I get questions from my customers that claim that they never received my automated emails. Note that I do not send more than 4-5 of those automated messages a day. So the outflow is very very low. The email itself is the registration instructions along with the registration code. So it shouldn't have anything too spammy in it.
So I decided to make a test. I used my own hotmail account to send a test email to. So I sent the first email. It never got into my inbox. I checked spam folder, inbox, been refreshing... nothing. I waited until the next morning. Still nothing. I then tried to send another email and in that case it made through to the same hotmail account just fine.
I then went to my control panel on the Mandrill web site and checked the "Outbound activity" and both of my test messages showed as "delivered", when the first one was clearly not. Worse still, it did not even show up in my Spam folder. It just disappeared without a trace.
So I'm curious, if anyone else had the same issue? And if so, how to address it?