From: Bridge Test <bridgetest@pm.test>
Date: 01 Jan 1980 00:00:00 +0000
To: Internal Bridge <bridgetest@protonmail.com>
Subject: Message with attachment name
Content-type: multipart/mixed; boundary="boundary"
Received: by 2002:0:0:0:0:0:0:0 with SMTP id 0123456789abcdef; Wed, 30 Dec 2020 01:23:45 0000

This is a multi-part message in MIME format.

--boundary
Content-Type: text/plain

Hello

--boundary
Content-Type: text/html; charset=utf-8
Content-Transfer-Encoding: 7bit

<h1> HELLO </h1>

--boundary
Content-Type: application/pdf; name="=?US-ASCII?Q?filename?="
Content-Disposition: attachment; filename="=?US-ASCII?Q?filename?="

somebytes

--boundary--