Device case studies

Manuals tell you where a setting should be. They don't tell you that a specific 2016 printer needs its certificate check turned off because its firmware never got a root certificate update — that only comes from someone who actually hit the problem on real hardware.

This page collects those reports: one device, one confirmed fix, credited to whoever found it.

Hitting a certificate error on a printer? Printer cannot verify the mail server certificate explains why a valid certificate gets rejected by older firmware, and what to do about it.

Case studies

Canon Maxify MB2755 — certificate verification must stay off, on either port

Reported by: @kevinbytnar

This 2016-era SOHO inkjet MFP fails certificate validation against mx.msgwing.com's Let's Encrypt certificate, because its firmware ships a fixed root CA store that predates modern Let's Encrypt roots — confirmed with openssl s_client and unchanged after a firmware update. Which exact chain the server presents can shift over time (an ECDSA chain through ISRG Root X2 as of this writing, an RSA chain through ISRG Root X1 earlier) — the printer's frozen trust store doesn't recognize either, so the fix is the same regardless: disable certificate verification on the device, on whichever port you use.

Full writeup, screenshots and the technical explanation: PRINTERS.md → Known exception: Canon Maxify MB2755.

---

Have a device with a similar quirk?

If you hit something on real hardware that isn't in PRINTERS.md — a certificate issue, a firmware bug, a menu that's in a different place than the manual says — report it:

• Open an issue or a pull request with what you found (a screenshot helps, with any account details redacted).
• Hardware-confirmed reports are worth more here than anything written from a manual, and get credited by GitHub username when added.

This list only grows if people who hit the edge cases report them — consider this an open invitation.