Re: mails get flagged in OutLook

On Mon, Feb 16, 2026 at 10:01:07PM +1100, raf via Mutt-users wrote:
> On Mon, Feb 16, 2026 at 08:28:44AM +0100, Nicola Pinna <nicola.pinna@hu-=
berlin.de> wrote:
>=20
> > <On Sat, Feb 14, 2026 at 06:15:26PM +0000, Nuno Silva via Mutt-users w=
rote:>
> >=20
> > > On 2026-02-09, Matthias Apitz wrote:
> > >=20
> > > > Hello,
> > > >
> > > > I'm adding to all my mails sent with mutt (like this one) two X-he=
ader
> > > > lines:
> > > >
> > > >     X-Operating-System: FreeBSD 14.0-CURRENT r1400094 (amd64)
> > > >     X-message-flag: Mails in HTML will not be read! Please, only p=
lain text.
> > > >
> > > > I got informed by an reader of a mailing-list that my mails get fl=
agged
> > > > in his OutLook mailbox with a small red flag. Technically this is =
added
> > > > by a Microsoft SPAM protection which adds into my mail a header am=
ong other
> > > > stuff a line like this:
> > > >
> > > > ```
> > > >     X-Microsoft-Antispam-Mailbox-Delivery:
> > > > 	ucf:0;jmr:0;auth:0;dest:I;ENG:(910005)(944506478)(944626604)(4710=
137)(4713098)(499
> > > > 9163)(920097)(930201)(20251009147)(140003);
> > > > ```
> > > >
> > > > I did tests with an OutLook destination I've access to and the "cu=
lprit"
> > > > seems to be only this X-header:
> > > >
> > > >     X-message-flag: Mails in HTML will not be read! Please, only p=
lain text.
> > > >
> > > > Any comments on what could he do or what could I do?
> > > >
> > > > Thanks
> > > >
> > > > 	matthias
>=20
> Hi,
>=20
> I expect that it's unlikely that recipients of your
> emails would see the X-message-flag header. I might be
> wrong, but many non-mutt mail clients I see don't show
> many headers at all (not even the From: header!). You
> have to out of your way to see them.
>=20
> It probably makes more sense to remove that header, and
> add your plea to your signature. That way, recipients
> can actually see it without additional/unlikely effort
> on their part.
>=20
> However, if you want to accept that other people will
> continue to do what they do, and you have no control
> over that, I have a program that might help you
> (raf.org/textmail). It converts HTML emails to plain
> text, and Excel attachments to CSV, and Word/PDF
> attachments to text, delete images, etc. If your email
> is delivered in a way that you can use procmail to
> filter it before it's saved, you could convert incoming
> emails to plain text before you see it.
>=20
> cheers,
> raf
>=20

Question here is whether you are going to adapt to some quirk in MS
Outlook, or just use mutt the way it is designed. There are a lot of
things where Microsoft software interpretes and displays things
differently from non-MS software. IMHO we shouldn't bow for that, nor
its users.

//meine