This article applies to:
- Trustwave MailMarshal (SEG)
Question:
- How do I block email where the SMTP "Mail From:" address is blank?
Symptoms:
- During the SMTP communications, a sending mail server will provide a blank 'Mail From' address (Mail From:<>).
- Messages with a blank "Mail From" can be generated by spam activity in some circumstances.
Procedure:
Emails that are sent with blank sender addresses can be blocked by creating and enabling a Connection rule.
Current versions of the product include a default rule 'Reject Messages with Blank Return Path' that is disabled by default
Important:
Before enabling such a rule, carefully review all information in this article.
If your installation was upgraded from an older version and does not include this rule, you can add it manually. See the current Default Rules document for a definition of this rule.
Notes:
Enabling this rule will make you RFC non-compliant. SMTP servers must accept mail with blank return paths for the purposes of handling their own NDRs and returned messages.
Be aware that turning on this rule could also result in your server being blocked as a "bad actor" by other server, if your server rejects messages that you are required to accept.
This rule can also interfere with sender verification techniques used by some other email software.
If you choose to block messages with blank "Mail From" you should only do so temporarily, and monitor activity closely.
See the following Trustwave Knowledgebase article for more information:
- Q11815 Why am I receiving a number of Non Delivery Reports (NDR)?
- This article was previously published as:
- NETIQKB41125