For anyone looking to send applications via certified snail mail or fax, I can recommend these two services after using them:
1.) Mailing physical letters: https://app.uploadletters.com/
Costs about $8.49/letter (I send 2-3 pages), and gives you a nice tracking page where you can monitor dates, view the file you sent, etc.
(picrel)
Some other services are priced around the same but I haven't tried them yet (this is about the cheapest I've seen for low-volume stuff).
2.) Fax: https://faxzero.com/
Lets you send faxes for free. (small volume of like 5 pages / day), perfect for job applicants.
Typically you might spent 4-10 cents / page for faxes through other services, so it's not really a big barrier if you see it on a job posting. You typically just upload a pdf, input their fax number, then click send. (Don't be mean and send them 1000 pages since it'll all print off at their fax machine).