How to block specific sender addresses.
One of the difficulties in blocking e-mail addresses is that there are
actually two sender addresses associated with a message. One address is
contained inside the headers of the message (i.e. in the message content itself,
on the From header line). The other address is the one that the remote mail
client or server sends in the SMTP conversation and is known as the
envelope sender. The envelope information can be seen by reviewing the SMTP
logs noting the MAIL FROM: commands in the logs. Or, in a received
email, it will be the email address in the Return-Path header
item. Blocking of an email based on the sender email address can be done
either using the global filters, with a criteria of checking the From and CC
addresses, or at the mailbox level, where users can block domains or addresses
via their webmail options.
A special kind of sender can also be used in the MAIL FROM command. This is called a null sender and is represented by no sender address (which looks like <> in the SMTP conversation). Null senders are used for system generated messages, such as delivery failures.
There is a Windows registry key which can be enabled to block these null senders, but it is not advised to enable, as it will affect delivery of system generated messages, and may lead you to be blocked by remote servers. There may be some cases where you need to block them, so the registry key is:
"Block null senders"=dword:00000001
Restart the SMTP service when changing or adding this registry key.
Tracking message path and sender location: Article ME020338
|Product:||MailEnable (All Versions)|
|Class:||HOWTO: Product Instructions|
|Revised:||Tuesday, January 21, 2020|