What is the best way to block inbound messages that are larger than 10MB -- and also make sure the sender knows that the message was refused by us?
I have an envelope notification that sends back a simple message to the sender, stating that the message violates our policy.
However it seems like I should be able to refuse the connection if its a certain size and let the sender's system handle the NDR. (In other words, let the sender's system tell the sender that his message was refused.)
Intrusion Defender -> SMTPI Service
Under the section called Connection Management there are two settings - SIZE Extension (MB) - External and SIZE Extension (MB) - Internal
External would be inbound messages
Internal would be outbound messages
The MEG would block messages by either the ESMTP code:
MAIL FROM: <firstname.lastname@example.org> SIZE=12345678
or the actual size of the message after it has been accepted in proxy.
The sending server would generate an NDR with an error that would be something along the lines of "550, exceeds size limit".