(No sender) on ESA/SMA

[spacemeb]

Hello,

We have received multiple messages some of them were malicious in which we could not see the sender's domain.

Instead of the sender we had the (no sender) entry.

Have you any idea where this is coming from? is it a bug ? or normal behavior under certain circumstances? 

[Udupi Krishna. · Accepted solution]

Empty sender is one of known behaviours observed in bounce emails. Mail logs or message tracking might show "<>" for envelope sender. If there are suspicious emails coming in with an empty sender, a good way to tackle is to have bounce verification enabled.

ESA can then determine if these emails with empty sender was a result of an outgoing email from your domain. This way it can categorise genuine and invalid/suspicious bounce emails