Hi.. Recently we were blocked from sending email to att customers but were able to resolve that. Although it isn't the easiest process, but at least att does make it possible to unblock.
Last week I realized we are now blocked from being able to send emails to Optimum.net customers as I found out from a long time customer.
I called Optimum and talked to them for some 40 minutes while they tried to help me. In a nutshell, I honestly think that this company has their security specifications wound so tightly that they have made it impossible to fix this problem. For instance when you send emails such as bidding notices or notices to customers if one customer in their system decides to put one of the emails in their spam folder, that more or less causes a block. The way he explained it to me was that it is our responsibility to find out which customer of our thousands and thousands of customers did this and inform them who it is in order to be unblocked!!! I am still having trouble understanding how anyone can expect this to be a realistic request!
At any rate if you do have optimum.net, most likely we are not going to be able to send you email. I strongly recommend that you get a different email source such as gmail.