Knowledgebase: Backup
When testing backup email, I am seeing a 450 error.
Posted by Darren Radsmith on 09 November 2005 12:02 AM

What you are seeing is not an error but a warning message. This is called greylisting.

Greylisting is a simple method of defending electronic mail users against e-mail spam. It is the best way of blocking most spam without using content filters, which can cause false positives. In short, a mail transfer agent that uses greylisting will “temporarily reject” (a 450 error code) any email from a sender it does not recognize. If the mail is legitimate, the originating server will try again to send it later usually within a few minutes, at which time the destination will accept it. If the mail is from a spammer, it will not be retried so the spam will not be relayed through our systems and on to your mail server.

Greylisting Wikipedia Article

How do I test backup email?

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