How to properly deny applicants.

[James Salazar]

I'm new to the landlording world and had a question about denying applicants. I recently put my duplex up for rent and have received many applications. I received an applicant who passes all the criteria and if everything checks out will be approving them today. However do I Legally have to deny and send out a letter to every other applicant who applied or can I simply put that the unit is no longer available for rent?