Posts by email NOT being posted.

I just got a Ping account and I posted a photo to my Flickr, Blogger and Facebook accounts.

My question is that I have sent 5 such posts during the past 24 hours and only the first one made it and got posted.

Also, three of my posts were sent from my Hotmail account. Is posting from Hotmail allowed?

Does anyone know why this should be the case? Am I doing something wrong.

By the way I would like Ping to post to my Ning accounts too. I have more than one there.

Thanks