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Spam filtering

Spam filtering #

Purelymail uses SpamAssassin to filter incoming mail. When we think a particular piece of mail might be spam, it gets put into your "Junk" folder, unless your webmail filters move it elsewhere.

Every piece of mail receives a "Spam score" that measures how confident the system thinks it is spam. The default threshold is "5". While there is currently no convenient way to adjust this, a webmail filter could examine the X-Spam-Status header and override the default decision.

What tests does SpamAssassin perform? #

Standard SpamAssassin tests check the content, formatting, and source of messages to gauge how spammy they look.

Additionally, the message is compared to a per-user database of past messages manually moved into and out of the Junk mailbox (i.e. marked Spam/Ham). This database will only begin to be used when it has 200 examples of both spam and non-spam emails.

In addition, Purelymail adds a few custom tests:

Host blocking #

Certain IPs on spam blocklists will receive a rejection at the sending stage- before the mail is received or scanned. This stops a significant amount of spam from ever being sent. If this happens to you in error, you may need to contact the blocklist mentioned in the rejection message for a delisting (but be aware that most listings are a result of your IPs sending spam).

Greylisting #

Some sending IPs that don't look like they should be sending mail may be subject to Greylisting, a technique of temporarily rejecting mail to lower the efficiency of spam servers. Greylisting is only applied to senders that don't look like they have unique reverse IP records or HELO records.

This may cause a delay in legitimate email delivery for the first time between any sender-recipient pair, or until the sending IP has gained enough reputation for Purelymail to skip the check.

But I'm still getting spam! #

This happens. We don't have a perfect system, and spammers are very persistent. If it helps, feel free to forward (as attachment preferably) the email to abuse@purelymail.com and we may be able to take a look.