When a message cannot be delivered by the mail server, non-delivery reports (NDRs) are sent to a message recipient. The Exchange server attaches the original message to the NDR message when it sends the message. Since this is the default setting, it may be modified.
Note: If you send a copy of the original message with the NDR, it may cause your server to be listed on backscatter lists and FEB.spamlab.com.
Sending servers are being blocked, blacklisted, or prevented from sending to AppRiver clients because of FEB.spamlab.com.
An administrator may designate a size limit for the original messages. If the messages are larger than the designated size limit, then it will not be attached to the NDR message. Please use the following steps to configure the limit:
1. Open the Registry Editor and point it to the following path:
2. If there is no Queuing key, then generate one.
2. Now, generate a REG_DWORD value called MaxDSNSize.
3. Enter the limit value (bytes).
4. Restart the SMTP service.