Tax Planning and Spousal Support/ Maintenance/Alimony Payments
Federal taxes must be paid on spousal support/maintenance/alimony in the year it is received. If taxes are not withheld, it is possible you will be required to pay taxes when filing quarterly returns. For those who pay maintenance under a divorce agreement, the payments may be deductible if certain requirements are met. Note that any payments you make to your spouse that are not required by agreement or decree, are not deductible as maintenance payments. You should always consult with a tax professional before agreeing to a settlement amount to ensure the most beneficial tax treatment possible.
Source: IRS PUB 504 Divorced or Separated Individuals.