Spam Filtering and Graylisting
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On July 26th 2009 Smile Internet implemented additional servers to provide better spam filtering. This service is now optional for all domain customers at Smile, but is enabled by default unless requested otherwise by the customer. These servers act as gateways to our network, and provide the following services:
Graylisting - a system where the mail server temporarily rejects the mail. If the sending server is following the proper email procedures it will try to send the mail again. The second time the server receives the message it will accept the mail and track that sending server as a good source for mail. Since most spam is sent from computers that are not proper mail servers, they do not follow the proper procedures and never try to send the mail again. Graylisting is very effective in blocking a large quantity of unwanted email. The downside to graylisting is that there can be a delay, depending on the settings of the sending mail server, while it is building the database.
rDNS Checking - This is a lookup of the reverse DNS of the mail server. All mail servers should have reverse DNS that matches their forward DNS. If that isn't the case, the mail is rejected. Since computers infected with trojans and viruses don't have reverse DNS configured, (this is something that needs to be done by their ISP) rDNS checking blocks a significant amount of unwanted email.
RBL - This a check Realtim blackhole lists. Smile's servers have been doing this for a number of years, however the new system checks some new blacklists.
SPF Checking - a system includes rules in the DNS describing what servers can send mail from a particular domain.
These factors together have, in our testing, reduced the quantity of unwanted email by a very large percentage. There will always be rare situations where "wanted"mail is getting blocked. Depending on the reason for the block, we have a number of possibilities to whitelist servers, email addresses, etc. to make sure you are receiving the mail you are supposed to be receiving.
The standard Smile spam filtering (that places [SPAM] in the subject line is still in effect)
If you have questions or comments, please submit a trouble ticket.
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