This has the effect of slowing down the performance of their mail servers to the detriment of all genuine users. It has similar implications for customers own mail servers but can incurr additional phone call charges where those customers use metered dial-up services and since they have limited bandwidth the perfomance implications can be much more severe. Cloud Nine's mail servers have always had a degree of security higher than that of most of our customers but what we have been finding is that spammers have increasingly been taking control of less secure client mail servers and relaying their mail through these and then onto our network since customers connect to our mail servers. This is essential since a single misconfigured client mail server can be hijacked by spammers. The effect of this is to force delivery of all our customers mail to our mail servers in the first instance, and then to our customers.
Junk mail is bounced before it gets anywhere near our customers servers for onward delivery.
This does not affect outgoing mail delivery. Customers can set their mail servers to send directly using DNS so they can still ship mail onto the Internet without touching our servers but this MUST originate from their local network since it cannot have originated from outside as a result of the block we have placed. The MAPS database contains details of blacklisted and open relay mail servers that are the source of most junk email. This should reduce the flow of junk email to our customers. Most spammers email servers don't have properly configured DNS info and they don't want to know where the mail originated.