No recognition of `mail.markdown` filetype

[madduck]

Describe the bug

I have my NeoVim configured to have Markdown injected into Mail, since I write all my emails in Markdown for post-processing. As a consequence, I set the filetype for a mail message to mail.markdown.

If I do so, then markdown-preview won't load the key bindings. The command :MarkdownPreview still works, but <leader>cp does not.

I have tried adding mail.markdown verbatim to g:mkdp_filetypes, but to no avail. In any case, since for Vim, mail.markdown is really mail & markdown, markdown-preview should load in its default configuration for filetype mail.markdown. That would be ideal.

To Reproduce

My setup is here: https://git.madduck.net/etc/lazyvim.git

The main file is .config/lazyvim/after/ftplugin/mail as it changes the filetype.

In my setup, <leader>cp is not available.

However, I could not reproduce this problem with `+"set ft=mail.markdown"`` or using a modeline.

Expected behavior

If I list markdown in g:mkdp_filetypes, then I expect markdown-preview to work if the filetype is mail.markdown

Desktop (please complete the following information):

• OS: Debian sid, Neovim 0.10.4-8, latest Lazyvim, latest markdown-preview