When do colleges mail out acceptance/rejection letters?

It depends on the school's admission process. If the school does Early Decision (binding) or Early Action (not binding), you should recieve a letter in December or January. If the school has rolling admissions, you should recieve a decision within a few weeks. Some schools with rolling admissions give priority to students who apply before a certain date. If a school has only one admission process and makes decions only one, you should expect to recieve a letter between mid-March to early-April and you usually have until May 1 to make a decision.