Over the past decade all of that snail mail went away. Covid expedited any of the hold-outs either at the high school or college level.
There are things that can/could be sent via mail, but then the college has an intern or staff who have to scan it in and match to the applicant.
To the OP, the school counselor or college coordinator or other support staff at the school will have access to the software that interfaces with the common app, colleges not in common app, etc… most of those systems require that person to log in and hit send in batches. The counselor will have the ability to review the teacher letter of recs before they are sent which can be helpful for new teachers who may not understand what is needed in those letters for the highly selective schools.
They will send the transcript from the end of the 11th grade year, one mid-senior year, and the final at the end.
Any DE college classes will need transcripts directly from the college. Your child will need to request those.
The other critical part is their recommendation form/letter. There are some common app questions that they answer for this.
And then they will assist with similar docs for some higher stakes scholarships that are separate from admissions.