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How to block incoming faxes based on sender number or TSI

Article # 3036012 - Page views: 59


Not only emails may contain spam messages, also faxes may be unwanted and can be labeled as spam. Therefore it might be interesting to block the reception of such spam faxes by blocking known senders directly. This article describes blocking the incoming fax all together, another option might also be to receive the fax and instead of routing it to the end-user route it to a so called NULL TUM channel effectively deleting it while producing costs for the sender. Blocking the fax all together is advised as receiving the fax of course also uses local resources during reception. (e.g. use of a fax channel during reception)


The solution is to tell TCOSS that the originator of the fax is invalid. On a technical note, we create a "bad originator" error in TCOSS so that the send order cannot be created and the fax is rejected.

If you block faxes in this way, the sender will get a fax interruption during the initial training phase of the fax. This means, the initial call is accepted and as soon as any data is to be received, TCOSS will close the connection. The sender will not get a Sent OK.

This can be done in two ways:

Option A:

In a default KCS environment, FAX (with prefix F:) is the originator service for inbound faxes as defined in TCOSS config line 235, position 3.
When assuming the above defaults you can block a specific Caller within the Arr99, **INBOUND section.

For example, if you want to block faxes from number 1234, you would need to add it to the Arr99 like this:


user "invalid" does not exist -> TCOSS will not accept the message.


  • It is quite simple to add new senders to this blacklist.


  • In the other routing sections within the Arr99 the F:1234 MUST not be modified. (Normalized)
  • If a user tries to send at fax to: FAX,1234 this will also fail.
  • When the sender blocks sending his Caller ID the TSI of the sender is used which can be faked, but can still be entered here if known.
Option B:

In addition to option A, you can also add the numbers to the fax channel configuration.

For example if you want to block numbers 1234 and 5678, you can proceed like this:

Enter within the fax channel configuration on a free line between 254-283:


Then, in the Arr99 you add the following


If the caller number is 1234 or 5678 it is routed to 0001, which is refused in the Arr99 similair to option A because "user" invalid doesn't exist. 


  • It is possible to send a fax to FAX,1234 and FAX,5678


  • If sender blocks his Called ID, you would have to enter the TSI instead.
  • Every time you enter a new number to the channel configuration, you must restart the node of these channels.
  • There is only a limited number of lines available in the number conversion table. (254-283)
  • The first match wins; if you have something like "3~=~" on a higher configuration line, blocking the number would not work.

Level of Complexity 


Applies to  

Product Version Build Environment Hardware
Kofax Communication Server All