> You have accurately described a email mailing list. Where in the value-add here?

Pre-prints are basically a mailinglist where you post your paper prior to peer review.

The value over a simple mailinglist is:

1. Stable URL and citation to enable other work and discussions to cite and reference it.

2. Versioning of the paper, allowing updates to be made without having mail out the paper, while allowing everyone to find all prior versions

3. Host for a PDF and data that might be quite large

4. Centralized searchable long term archive of scientific papers

5. Scalability, arxiv gets 30,000 submissions a day, no one wants to receive 30,000 PDFs in their inbox everyday