Whether it will negatively impact your application depends on the schools you applied to. Some will not review your application until it is "complete," meaning secondary submitted, fee paid, and LORs in. Others only require a certain number of LORs to be in before they review it. Likely, this will further delay your application being reviewed, which is far from ideal.
See if there's anyway to get the letters uploaded electronically, as that is much faster and doesn't depend on the USPS.
Yeah I just asked my school to send them again today. This letter was the only one that was abnormally late due to system glitches according to my school. The other letters and apps were in since a month ago...
Yeah. It's probably lost if it hasn't been in for a month. Also, I thought 3 letters or 4 letters is the minimum for schools. Hopefully, your schools started to review your application without that letter.