Content filtering is done to avoid the reception of bulk or spam mail in the mailboxes of our customers. Although the antispam engine uses much more complex rules, recommendations as the following ones can help:
- Restrict the use of words or sentences usually involved in spam campaigns.
- Avoid sending messages that only contain an image.
- Avoid sending messages that contain HTML forms, flash or active-x object, and the like.
- Do not send attachments with extensions usually used by viruses, such as: .scr, .pif, .vbs, ...
- Do not send attachments with executable extensions (can be sent inside file bundles cyphered with password).
- Avoid the use of links or redirections that may look like phishing in those messages.
- In distribution lists, send messages only to subscribed users.
- In distribution lists, add links for helping the unsubscription from those lists in the messages sent.
- Send messages with a correct and error-free SPF record and valid DKIM signature.
- Send messages from a domain of the FROM header address that exists and resolves correctly.
- Send messages from an IP with an existing PTR (reverse resolution).
Antispam systems are also sensitive to sudden changes in the volume of messages sent from a certain account or IP. We advice against doing one-time bulk deliveries, but instead splitting that delivery into time-separated and smaller deliveries.