Technical details on how Anti-spam filters work

MX Records

Anti-spam filtering is enabled by changing the domain's MX records to route incoming emails to the filtering servers first before passing the message off to the MX machines for delivery. Domains using non-DreamHost nameservers will need to manually update their MX records to reflect the change.

The filter records are:

  • 0 mx1.mailchannels.net
  • 0 mx2.mailchannels.net

Special considerations for forwarding addresses

There are certain things to remember with filtering in relation to forwarding email addresses. The details for the four combinations with this setup are outlined below:

  • If the domain is being filtered, and the address is being forwarded to another DreamHost email address that is also filtered, then email gets sorted based on the filter mail settings of the original forwarding address.
  • If the domain is being filtered, and the address is being forwarded to another DreamHost email address that is not filtered, then the email will be filtered.
  • If the domain is being filtered, and the address is being forwarded to an outside address only (like @gmail), then the filter settings for the outside address will be used.
  • If the domain is not being filtered and it forwards to a DreamHost email address that is on a filtered domain, then the email will not be filtered.

The following table shows how Anti-spam filtering works for/with forward-only addresses. A@example.com is forward-only and sends emails to B@example.net which is a fully hosted mail account:

A@example.com uses filtering B@example.net uses filtering Is filtering done on incoming mail? What filter is used?
Yes Yes Yes A@example.com
Yes No Yes A@example.com
No Yes No N/A
No No No filtering done N/A

Filtering and what it does

There are two services currently set up to filter spam. Below is a description of each:

MailChannels (enabled as of September 2020)
MailChannels is DreamHost's Cloud-based mail filter. It accepts and evaluates mail, adds a specific header for spam messages, then relays messages to MX servers.
Procmail
This is the delivery agent for the mailbox, which only places mail in the Spam folder and rejects blocked senders when it detects MailChannels headers. This is also responsible for the user-defined filters defined in the panel. 
Vade (soon to be disabled)
Vade is DreamHost's soon-to-be-former mail filter. Vade will no longer work after March 23, 2021. 

See also

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