This is better than some of his other stuff. But he missed a few things:

OnionMail server configurations vary. Not all instances use POP3 on port 110 or SMTP on port 25 with STARTTLS; some require SSL/TLS on ports 995 (POP3S) or 465 (SMTPS). Consult each server’s configuration page / directory entry and apply those parameters.

Tor Browser alone does not expose a system-wide SOCKS5 proxy, so Thunderbird cannot route traffic through Tor by default. Consider running the Tor service (Tor Expert Bundle or tor daemon) and configure the client to use 127.0.0.1:9050 (SOCKS5).

STARTTLS support on .onion services is inconsistent and oft replaced with self‑signed or plaintext connections. Confirm certificate validity and opt for native SSL/TLS or end‑to‑end encryption.

Finally, depending on your chosen server, both POP3 and IMAP may be supported.