Milton,

SpamFilter will never send an email back to the sender when an email is rejected. Instead, SpamFilter will reject spam emails with an SMTP error message. This causes the remote server to send an NDR email to their customer (the sender) to notify them the email was rejected. Please note that, when an email is blocked, the sender *must* be notified to inform them of the delivery problems. If not, the sender will not know an email was blocked, and the recipient will never see the email unless they look in their quarantine (but this defeats the purpose of a spamfilter, if we require users to continuously check their quarantined emails anyways...).

This said, if admins are absolutely certain they do not want SpamFilter to cause andy NDR emails back to the sender, the following option is available in the SpamFilter.ini file to prevent this:

;Setting DoNotSendNDROnQuarantine to 1 will prevent generation of NDR when email are quarantined by causing SpamFilter *not* to send an error code when quarantining emails

DoNotSendNDROnQuarantine=0