How can i block a junk fax number in a hp j3640 thanks in advance

The officejet is not smart enough to block faxes, you need to do that thru your phone company, some companies let you block numbers by a few keystrokes at your phone.

Set the junk fax mode
By default, Block Junk Fax mode is turned On . If you do not subscribe to a caller ID service through your phone provider, or do not want to use this feature, you can turn off this setting.
To set the junk fax mode
Press Setup .
Press the right arrow to select Basic Fax Setup , and then press OK .
Press the right arrow to select Junk Fax Blocker Set Up .
Press the right arrow to select Block Junk Fax the press OK .
When prompted, press 1 for Yes or 2 for No .
Add numbers to the junk fax list
There are two ways to add a number to your junk list. You can select numbers from your caller ID history, or you can enter new numbers. The numbers in your junk list will be blocked if Block Junk Fax mode is set to On .
To select a number from the caller ID list
Press Setup .
Press the right arrow to select Basic Fax Setup then press OK .
Press the right arrow to select Add Number to Junk List , and then press the right arrow to select Number and then press OK .
Press the right arrow to scroll through the numbers from which you have received faxes. When the number you want to block appears, press OK to select it.
When the Select Another? prompt displays, do one of the following:
If you want to add another number to the list of junk fax numbers , press 1 to select Yes , and then repeat step 4 for each number you want to block.
If you are done , press 2 to select No .
To manually enter a number to block
Press Setup .
Press the right arrow to select Basic Fax Setup press OK .
Then press the right arrow to select Junk Fax Blocker Set Up and then press OK .
Press the right arrow to select Add Number to Junk List press OK , and then press the right arrow to select Enter Number .
Use the keypad to enter a fax number to block and then press OK . Make sure you enter the fax number as it appears on the display, and not the fax number that appears on the fax header of the received fax, as these numbers can be different.
When the Enter Another? prompt displays, do one of the following:
If you want to add another number to the list of junk fax numbers , press 1 to select Yes , and then repeat step 4 for each number you want to block.
If you are done , press 2 to select No .
Remove numbers from the junk fax list
If you no longer want to block a fax number that number can be removed from the junk fax list.
To remove numbers from the junk fax list
Press Setup .
Press the right arrow to select Basic Fax Setup then press OK , and then press the right arrow again to select Junk Fax Blocker Set Up then press OK .
Press the right arrow to select Remove Number from Junk List .
Press the right arrow to scroll through the blocked numbers. When the number you want to remove displays, press OK to select it.
When the Delete Another? prompt displays, do one of the following:
If you want to remove another number from the list of junk fax numbers , press 1 to select Yes , and then repeat step 4 for each number you want to block.
If you are done , press 2 to select No .
If you subscribe to a caller ID service through your phone provider, you can block specific fax numbers, so the HP Fax does not print faxes received from those numbers in the future. When an incoming fax call is received, the HP Fax compares the number to the list of junk fax numbers you set up to determine if the call should be blocked. If the number matches a number in the blocked fax numbers list, the fax is not printed. (The maximum number of fax numbers you can block varies by model.)
Thank you.

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Why not try LEO Privacy? There is a funcrion which name Harassment Interception, you can use this applock to block certain unwanted calls, this is very helpful for me. Hope this applock can also help you.
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