Cannot send to mailing lists - client host rejected: cannot find your hostname

I'm having a minor problem with posting to the list. I have my own mail server using postfix, fetchmail, and courier. I have several domain names, and I'm using one for my mail server. In my logs I'm seeing 450 errors for freebsd-questions since around the end of last year, but I did have

Re: Cannot send to mailing lists - client host rejected: cannot find your hostname

I'm having a minor problem with posting to the list. I have my own mail server using postfix, fetchmail, and courier. I have several domain names, and I'm using one for my mail server. In my logs I'm seeing 450 errors for freebsd-questions since around the end of last year, but I did