Here are several samples of valid and invalid email reaction messages.
Valid multipart/alternative
Email reactions usually have three parts:
text/plain: the plain text version of the message.text/vnd.google.email-reaction+json: the reaction part.text/html: the HTML version of the message.
Here's an example:
From: [email protected]
Message-ID: <[email protected]>
Subject: subject
MIME-Version: 1.0
In-Reply-To: <[email protected]>
Content-Type: multipart/alternative;
boundary="----=_Part_0_2012232625.1697791227635"
------=_Part_0_2012232625.1697791227635
Content-Type: text/plain; charset=us-ascii
Content-Transfer-Encoding: 7bit
Text body content
------=_Part_0_2012232625.1697791227635
Content-Type: text/vnd.google.email-reaction+json; charset=UTF-8
Content-Transfer-Encoding: quoted-printable
{"emoji":"=F0=9F=99=83","version":1}
------=_Part_0_2012232625.1697791227635
Content-Type: text/html; charset=UTF-8
Content-Transfer-Encoding: quoted-printable
<h1>HTML body content</h1>
------=_Part_0_2012232625.1697791227635--
Single valid body part
Email reactions can also just have a single body part like:
From: [email protected]
Message-ID: <[email protected]>
Subject: subject
MIME-Version: 1.0
In-Reply-To: <[email protected]>
Content-Type: text/vnd.google.email-reaction+json; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable
{"emoji":"=F0=9F=99=83","version":1}
Note that the Content-Transfer-Encoding can be any standard encoding:
From: [email protected]
Message-ID: <[email protected]>
Subject: subject
MIME-Version: 1.0
In-Reply-To: <[email protected]>
Content-Type: text/vnd.google.email-reaction+json
Content-Transfer-Encoding: base64
ewogICJlbW9qaSI6ICLwn46JIiwKICAidmVyc2lvbiI6IDEKfQ==
For binary encodings, like base64, the JSON must be encoded as UTF-8.
Valid nested multipart/alternative in multipart/related
If the reaction is to a message that had inline attachments, it's possible to
generate a message with a multipart/related body part that contains the
attachments plus a multipart/alternative part like the previous example.
From: [email protected]
Message-ID: <[email protected]>
Subject: subject
MIME-Version: 1.0
In-Reply-To: <[email protected]>
Content-Type: multipart/related;
boundary="----=_Part_0_2012232625.1697793303618"
------=_Part_0_2012232625.1697793303618
Content-Type: multipart/alternative;
boundary="----=_Part_1_984213526.1697793303621"
------=_Part_1_984213526.1697793303621
Content-Type: text/plain; charset=us-ascii
Content-Transfer-Encoding: 7bit
Text body content
------=_Part_1_984213526.1697793303621
Content-Type: text/vnd.google.email-reaction+json
Content-Transfer-Encoding: base64
ewogICJlbW9qaSI6ICLwn46JIiwKICAidmVyc2lvbiI6IDEKfQ==
------=_Part_1_984213526.1697793303621
Content-Type: text/html; charset=UTF-8
Content-Transfer-Encoding: quoted-printable
<h1>HTML body content</h1>
------=_Part_1_984213526.1697793303621--
------=_Part_0_2012232625.1697793303618
Content-Type: text/vnd.google.email-reaction+json
Content-Transfer-Encoding: base64
Content-Disposition: attachment; filename="1x1.png"
iVBORw0KGgoAAAANSUhEUgAAAAEAAAABAQMAAAAl21bKAAAAA1BMVEUAAACnej3aAAAAAXRSTlMA
QObYZgAAAApJREFUCNdjYAAAAAIAAeIhvDMAAAAASUVORK5CYII=
------=_Part_0_2012232625.1697793303618--
(Note that the multipart/related body part should have other fields as
specified by RFC2387 but those are irrelevant for
determining whether an email reaction is valid.)
Invalid JSON format
The following reaction is invalid because the JSON is missing the closing brace:
From: [email protected]
Message-ID: <[email protected]>
Subject: subject
MIME-Version: 1.0
In-Reply-To: <[email protected]>
Content-Type: text/vnd.google.email-reaction+json; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable
{"emoji":"=F0=9F=99=83","version":1
The following reaction is invalid because the JSON has a trailing comma:
From: [email protected]
Message-ID: <[email protected]>
Subject: subject
MIME-Version: 1.0
In-Reply-To: <[email protected]>
Content-Type: text/vnd.google.email-reaction+json; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable
{"emoji":"=F0=9F=99=83","version":1,}
Invalid version field
The following reaction is invalid because it's missing the version field:
From: [email protected]
Message-ID: <[email protected]>
Subject: subject
MIME-Version: 1.0
In-Reply-To: <[email protected]>
Content-Type: text/vnd.google.email-reaction+json; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable
{"emoji":"=F0=9F=99=83"}
The following reaction is invalid because the version field isn't 1:
From: [email protected]
Message-ID: <[email protected]>
Subject: subject
MIME-Version: 1.0
In-Reply-To: <[email protected]>
Content-Type: text/vnd.google.email-reaction+json; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable
{"emoji":"=F0=9F=99=83","version":2}
Invalid emoji field
The following reaction is invalid because the emoji field is empty:
From: [email protected]
Message-ID: <[email protected]>
Subject: subject
MIME-Version: 1.0
In-Reply-To: <[email protected]>
Content-Type: text/vnd.google.email-reaction+json; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable
{"emoji":"","version":1}
The following reaction is invalid because the emoji field doesn't contain a
valid emoji.
From: [email protected]
Message-ID: <[email protected]>
Subject: subject
MIME-Version: 1.0
In-Reply-To: <[email protected]>
Content-Type: text/vnd.google.email-reaction+json; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable
{"emoji":"A","version":1}
The following reaction is invalid because the ❤ emoji is missing between the two zero-width joiner (ZWJ) characters. Note that the = character at the end of the first content line represents a soft line break in the Quoted-Printable encoding.
From: [email protected]
Message-ID: <[email protected]>
Subject: subject
MIME-Version: 1.0
In-Reply-To: <[email protected]>
Content-Type: text/vnd.google.email-reaction+json; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable
{"emoji":"=F0=9F=91=A9=F0=9F=8F=BC=E2=80=8D=E2=80=8D=F0=9F=91=A8=F0=9F=8F=BE",=
"version":1}