Install the new signature
Steps 1 and 2 are on the kit page. On your computer, open https://pmd-email-assets.pages.dev/, type your details and press Copy. Then follow Steps 3 and 4 below.
Works in Outlook, Mail and Gmail. Fill in the form, press Copy, then follow the short steps for your app. The logo loads from the web, so it stays sharp and never travels as an attachment.
Preview
Thanks, the proof is attached.
If copying is blocked, select the signature in the preview. Press Ctrl+C on Windows or Cmd+C on a Mac.
Do not use Insert, Pictures, Inline. That stores the logo inside the signature, which is what broke the old one.
Another route: select File, Options, Mail, then Signatures.
Phone apps take the plain-text version. Press Copy plain-text version in step 2 first. If you copy on a computer, email the text to yourself and copy it on the phone.
https://pmd-email-assets.pages.dev/pmd-signature-logo-v6.pngExchange can add the same signature to every outgoing message with a mail flow rule. Because the server adds it, no editor strips the dark-mode code. Microsoft's page confirms the rule accepts HTML, inline CSS, images through the IMG tag and per-user tokens such as display name. It lists limits: server signatures do not appear in Sent Items, images cannot be embedded, and PowerShell allows 5000 characters.
Not yet tested: whether Exchange keeps the style block that holds the dark-mode switch. IT should test one rule on one mailbox first. Do not paste this template into an app's signature box, because the box removes the switch.
Not yet tested in the real app: Outlook for Windows, Outlook for Mac, Mail on Mac, Mail on iPhone, Gmail and the phone apps. Steps for those apps follow the vendor pages above.