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anti-spam_protections

Anti-Spam Protections

The SoAustin anti-spam strategy is to employ multiple methods to reduce spam, but not at the risk of “false positives” (classifying good mail as spam).

This note lists the methods we're using.

Contact postmaster@soaustin.net if you have questions or feedback.

Block Lists

SoAustin uses spam block lists to refuse email from known spam sources.

We use the following block lists:

Greylisting

Greylisting is an anti-spam technique that reduces spam from spambots. We implement limited greylisting, depending on the country of origin.

How greylisting works: The first time you receive mail from a never-before-seen sender, that mail is temporarily rejected by the server and the sender is added to a greylist. The remote mail server will try to deliver the message again sometime later – typically between 5 and 30 minutes later. When that happens, the mail is accepted by our server, and the sender is removed from the greylist. The message is then delivered.

The server remembers senders who pass greylisting for at least a month, so if they send you mail again it will not be subject to greylisting.

Greylisting works because spambots typically are badly built mail servers that do not retry after a message fails.

At this time, mail originating from the following countries is not subject to greylisting and will be delivered without delay (even if it's spam):

  • AU - Australia
  • CA - Canada
  • DE - Germany
  • DK - Denmark
  • GB - Great Britain
  • IE - Ireland
  • NL - Netherlands
  • NZ - New Zealand
  • SE - Sweden
  • UK - United Kingdom
  • US - United States

Mail that originates from any other country will be subject to greylisting.

Origination is determined by the location of the sending email server, not email address.

The greylisting feature is new (added Nov 2016), and will be adjusted as needed to improve spam blocking without incurring excessive delays.

Filtering

All incoming mail is processed by SpamAssassin (https://spamassassin.apache.org/).

SpamAssassin examines each incoming mail message and assesses a spam score. In our configuration, a score of 6.0 or higher is considered spam. (This is conservative – the SpamAssassin default is 5.0.)

When a message score exceeds this threshold, the message is filed in a separate folder named Junk rather than your main inbox. If you use IMAP to access your email, you can view the messages filed as Junk.

Advanced: SpamAssassin Configuration

Advanced users may choose to tune their SpamAssassin settings.

  • Log into your account on shell.soaustin.net using an ssh terminal application.
  • Edit your Mailbox/.spamassassin/user_prefs file.

Information on preference settings here: https://spamassassin.apache.org/full/3.1.x/doc/Mail_SpamAssassin_Conf.html

The above anti-spam methods catch a lot of spam … but not all spam. Once again, we don't want the server to be so aggressive that it throws away good mail.

You can help minimize spam if your mail-reading program includes anti-spam features, such as the junk mail filter Thunderbird offers. The filter built into a mail-reading program typically trains itself on your incoming mail to better distinguish good email from spam. If you use Thunderbird or something similar, we recommend that you enable the junk mail filter.

anti-spam_protections.txt · Last modified: 2016/11/20 21:44 by admin