I sent a newsletter to a subscriber list of 597 subscribers 3 days ago, I throttled the sending to 70 emails every 15 minutes as my host has a limit of 350 per hour. I used php to send.
On this mail out I have an unopened rate of 99.3 percent!!!
To check what is happening I created a new list with one subscriber, me at a yahoo account. I sent the same newsletter to this list of one.
It sent but went straight to spam box in yahoo.
Do you think this might have been what happened to the 593 that were not opened or could there be a problem in sending limits?