A customer contacts and tells that someone has sent an email, but they have not received it. ”A message blocked by filtration” (or ”we have troubles to receive email/emails are delayed…”).


D-Fence services works so that;

1) email is relayed to the receiver with all attachments

2) email is rejected to the sender with NDR

There will be no delay what so ever in these transactions.

The problem is settled with the following procedure:

a) Has the sender received an error notification (NDR) from D-Fence, saying that we have blocked your mail, because it has been decoded as a virus or spam?

b) Has the sender received any error notifications? If yes, what does it say?
(sample of NDR » )

c) Please check if there is ”left over spam filtering mechanism” active in clients end, which has sent the message to ”spambox” or ”deleted box”. If there is still this kind of configuration, please remove it.

d) In some cases the receiver servers firewall either delay or block email messages. Check clients firewall and it’s software version »

e) Malfunctions in the sending server can cause delays or total rejects in email messaging. Please stay in SMTP specs and RFC standard to avoid any kind of mistakes, like 450 re-sending fails »

f) The sending end is misconfigurated (online scanners etc.) more »

To fix the problem:
Error notifications (NDR) are a good means to find out, what exactly has happened. The notification is unconditional.

Point A: if the sender has received a notification from D-Fence, it tells the reason why the mail has been blocked. The correct sender address/domain should be added to the ”White list”, and the problem of decoding as spam mail is eliminated.

If the mail is too big (over 30 MB), ask the customer to use the FTP protocol intended for sending this kind of files, or to wrap the message and send again. Requests for white-listing may also be sent to the address info@d-fence.fi


If the sender has received a failure notification from elsewhere than D-Fence, the mail has stopped somewhere else for the reason indicated in the failure notification. In this case the filtering has nothing to do with it.

Point B, if the sender has not received a failure notification, then all investigations along the years have shown it to be caused either by the

1) sending server (the mail has not been sent or/server’s configurations are non-standard /
Exchange SP2 problem)

2) destination server (malfunction, the mail is in the server, but not going to the inbox or goes to ”spambox”)

Our filtering services have proven to be significantly reliable. All relevant mail arrives and spam is blocked. Practice has proven that in our case the rate of default settings ”false positive” has been less than 1 / 1000 million.