[MlMt] Content-type markup=markdown and Microsoft/Yahoo Mail filtering

[Filip Stokkeland]

Hi!
I discovered something interesting with Outlook and Yahoo Mail's
junk filtering.

If I send to an Outlook.com address with markdown selected in
MailMate's composer, it's treated as junk on the Microsoft end.
And similar result with Yahoo Mail.

It seems like the issue is this header.
`Content-Type: text/plain; markup=markdown`

I'm not sure why, it doesn't make sense to me.
(Why should `markup=markdown` make a difference to the junk filter?)

But if I select just Plain text in the Composer, and if I even
add weird/utf-8 (Scandinavian) characters, then it works.
The email is **not** treated as junk.

This is the header then:
`Content-Type: text/plain; charset=utf-8; format=flowed`

(I used the same SMTP server, which had no issues with
blacklisting/reputation, SPF and DKIM properly verified. I can
share details/headers privately if you should be interested.)

(I don't need a debate around this, just thought my findings might
be of interest for someone ... It led me to set Plain text as
default when sending to some recipients.)

-- 
Filip
PS! Mailmate is so great! Thanks/mange takk Benny! (I wonder if
it will work well for a non-tech person. I'll let my dad test it,
he's not very satisfied with the newer layout etc in Mail.app.)
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