To begin, I have 2 email accounts.  One is thru my ISP - pa.net; the other is a gmail account.

My brother has 2 email accounts. One is thru Safe-mail.net; the other is thru programmer.net

I am having trouble receiving email from my brother.  Specifically, when he sends email from his safe-mail account to my pa.net account, it does not arrive.  I can send email from my pa.net account to his safe-mail account, and he will receive it; however, it does not work in reverse.

Two days ago, I sent him an email from my pa.net account to his safe-mail account.  I also sent his a text letting him know that I had sent it. He hit "reply" and sent me a reply. I never received it.

Last night, he decided to send 4 emails as a test: (1) from his safe-mail account to my pa.net account; (1) from his safe-mail account to my Gmail account; (1) from his programmer.net account to my pa.net account; and (1) from his programmer.net account to my gmail account.  I received 3 out of 4. The only one I did not receive was the one from his safe-mail account to my pa.net account.  

This AM I decided to email Tech Support at my ISP to see if they had a record, and whether the email from Safe-mail was being blocked.  They responded they had a record that my pa.net account had received an email from programmer.net, but no record of an email from safe-mail.net reaching their server.  They also said they do not have a block on anything coming from safe-mail.net.

Tonight my brother sent a test email from his safe-mail account to his programmer.net account. Then he forwarded that email from his programmer.net account to my pa.net account.  I received it.

Puzzling......  does anyone have an idea what is going on here?