If a business knows the address they have on file for a customer is wrong, does the business still have to mail the tax form to the wrong address regardless, so that the IRS sees an attempt was made?

I don't think that the tax forms should be mailed out to a knowingly wrong address, but I don't see anything on the IRS website that mentions this.

This is all I've found on the IRS.gov website:

Undeliverable Forms W-2.

Keep for 4 years any employee copies of Forms W-2 that you tried to but could not deliver. However, if the undelivered Form W-2 can be produced electronically through April 15th of the fourth year after the year at issue, you do not need to keep undeliverable employee copies. Do not send undeliverable employee copies of Forms W-2 to the Social Security Administration (SSA).
Employee's incorrect address on Form W-2.

If you filed a Form W-2 with the SSA that reported an incorrect address for the employee, but all other information on the Form W-2 was correct, do not file Form W-2c with the SSA merely to correct the address.
However, if the address was incorrect on the Form W-2 furnished to the employee, you must do one of the following.

• Issue a new, corrected Form W-2 to the employee that includes the new address. Indicate “REISSUED STATEMENT” on the new copies. Do not send Copy A of Form W-2 to the SSA.
• Issue a Form W-2c to the employee that shows the correct address in box i and all other correct information. Do not send Copy A of Form W-2c to the SSA.
• Reissue the Form W-2 with the incorrect address to the employee in an envelope showing the correct address or otherwise deliver it to the employee.

welcome to BOL with your first post!

why would you knowingly mail anything to a client when you know you have an invalid address for them, tax form or otherwise? if you know the address is bad, it meets the undeliverable definition, in my opinion (but you can certainly contact your local IRS office and ask that same question of them). try and get the proper address and move one.