There are two reasons why you may be getting the above error in response to messages you’ve sent to addresses on domains hosted by NinerNet, likely your own domain:
- It may be because you’re sending from an address on a domain that we host, but instead of sending your email through our SMTP server (smtp.niner.net) you’re sending through another SMTP server, possibly that of an ISP or another email service provider. In some cases this can happen because of a situation similar to that described in the sixth bullet point of our post “NC036: Migration update 20 — Solutions“, where you’ve sent the email through a third party, perhaps an ISP, or an email account you have with another provider.
- If you’re using some cloud-hosted application that tries to send email to you as you (or another user on your own domain), then that email looks like spam to the mail server, because lots of spammers mistakenly try to get their email through by sending their spam from your email address to your email address, or from another address on your own domain to you.
The solutions are, respectively (and respectfully):
- Configure your email program to use smtp.niner.net to send email from any domain that we host. If you’re following the configuration instructions we send you, then that is the case by default, and always has been.
- Have the provider of the cloud service send those emails from an address — even a “no-reply” address — on their own domain, or use SMTP AUTH to send the email through smtp.niner.net from an address on your own domain, just as you or any other human with an address on your domain would.
