Final answer:
If a return is identified as including an unallowable item, the IRS computes the necessary adjustment in taxes, and the taxpayer is notified by mail.
Step-by-step explanation:
If a return is identified as including an unallowable item, the IRS computes the necessary adjustment in taxes, and the taxpayer is notified by mail. This means that the IRS will calculate the appropriate changes to the tax amount and inform the taxpayer through a mailed notification. It is important for taxpayers to review the notification and understand the adjustments made by the IRS.