451 Recipient refused. Temporary mail refusal

[alan@isia.net]

451 Recipient refused. Temporary mail refusal. I do not get this response all of the time. But enough that it's driving me insane. Where should I look to solve this problem?

[alan@isia.net]

This message was created automatically by mail delivery software.

A message that you sent could not be delivered to one or more of its recipients. The following addresses failed:

<nvenditti@inste.edu>

SMTP error from remote server after RCPT command:
host mail.inste.edu[209.234.79.249]:
451 Recipient refused. Temporary mail refusal, please try again shortly.
retry timeout exceeded

this user exists in my email server. and it's correctly spelled. Help?

[rob]

The error message is part of the grey listing SPAM feature, and so may indicate your grey listing may need adjusting. Basically the default behaviour of grey listing is to block mails for up to 1 hour initialy from new IP's, then allow mails through if they try again within a few hours. Simply, you can reduce the intial 1 hour to 1 minute and increase the allow time (to better accomdate mail servers that dont retry for very long) or alternatively disable grey listing.

[alan@isia.net]

I understand what your saying. I will do that. I do have a question about the Grey List Safe IP's box. How would I include a whole domain in that list?

[rob]

This could be done in 2 ways, the first is that you simple use the white list option on the 'SPAM Filtering' tab (disable all SPAM filtering for that domain), and white list all senders from that domain with the format...

*@domain.com

Alternatively if you just want to use the grey listing option, then you should use the reverse IP lookup and enter the domain in the format...

*.domain.com