From the post linked to in the previous post in this thread:
From Crowdstack Tech Support:
I did some checking and it does not look like your server IP has been added to any mail blacklists. However, the mail log shows that the Yahoo mail servers are deferring emails from your server. This will affect anyone with an email address that uses Yahoo's mail servers including Yahoo, AOL, and Verizon.
There really is not anything we can do about this, it is just Yahoo being Yahoo. The emails usually hang out in the mail queue for a couple of days and then will be delivered and hopefully, Yahoo will stop deferring the emails at some point.
To be clear, this is not an OGR Forum problem. It is Yahoo holding emails in their queue for some reason only they know. Yahoo is notorious for doing this. I would suggest you get another email address from your local ISP, your own domain (if you have one) or from one of the other email providers like Hotmail, Gmail, etc.
I’m sorry, but there is nothing we can do from our end to fix this.