FYI I just went to Udon Immigration with a COVID letter from U.S. Embassy via email (also printed it out in color) and they said it had to be an original document via post mail lol... I asked the U.S. Embassy but no reply yet, I doubt they will offer that. Police were grumpy today and I pushed a few times to be sure... not sure if their excuse is accurate or just bullshit trying to delay dealing with these.
Update: U.S. Embassy replied to me and were surprised, and said Thai Immigration offices are supposed to accept the digital/printout versions of letters.