Proton Mail (Bridge) sends quoted strings with not allowed bytes

[soywod]

Given the following malformed message:

Date: Sat, 17 Aug 2024 12:21:18 +0000
From: "Bàd" <from@localhost>
To: "Wrȯng" <to@localhost>
Subject: All is wrong?

Too bad.

When fetching the envelope associated to this message from Proton Bridge, it returns a FETCH containing envelope address with not allowed bytes inside quoted strings, which leads to imap_next error Received malformed message.

I did the same test with Gmail, Outlook, Posteo and even 163, they all encode correctly the sender. Proton Bridge seems to send back envelope addresses as they are in the original message.

CC @duesee

[soywod]

I precise that the error occurs only from Proton Bridge (v3.6.1 tested). The malformed message displays correctly in their web interface.

[chibenwa]

CF https://datatracker.ietf.org/doc/html/rfc5738

They take it for granted and activated by default?

How they handle UTF 8 in mailbox names ?

[soywod]

In fact, Proton Bridge sends invalid bytes even when the message is correctly encoded. With From: =?utf-8?q?Cl=C3=A9ment_DOUIN?= <clement.douin@localhost>, I get the same error:

* 2 FETCH (UID 4 FLAGS (\\Seen) ENVELOPE (\"Thu, 22 Aug 2024 07:48:03 +0000\" \"Test\" ((\"Clément DOUIN\" NIL \"clement.douin\" \"localhost\")) ((\"Clément DOUIN\" NIL \"clement.douin\" \"localhost\")) ((\"Clément DOUIN\" NIL \"clement.douin\" \"localhost\")) ((NIL NIL \"pimalaya.org\" \"proton.me\")) NIL NIL NIL \"<2087a3200a5a1f8f27bcb2add236e70d@localhost>\") BODYSTRUCTURE (\"text\" \"plain\" (\"charset\" \"utf-8\") NIL NIL \"quoted-printable\" 7 1 NIL NIL NIL NIL))\r\n

They take it for granted and activated by default?

Looks like. I precise that I do not send any ENABLE UTF8.

How they handle UTF 8 in mailbox names ?

I created a folder named Envoyés, and looks like they properly encode it using UTF-7 as defined in https://www.rfc-editor.org/rfc/rfc3501#section-5.1.3.

event: Ok(
    DataReceived {
        data: List {
            items: [
                Unmarked,
            ],
            delimiter: Some(
                QuotedChar(
                    '/',
                ),
            ),
            mailbox: Other(
                MailboxOther(
                    String(
                        Quoted(
                            Quoted("Folders/Envoy&AOk-s"),
                        ),
                    ),
                ),
            ),
        },
    },
)

[soywod]

Looks like they also return invalid bytes in NO errors. Trying to create a mailbox Bàd leads to MalformedMessage error 0.1 NO invalid mailbox name [\"Bàd\"]: operation not allowed\r\n.

[soywod]

Looks like Proton Bridge does not support the ENABLE capability. And if I still try to enable it, I get once again a MalformedMessage error: 0.1 BAD [Error offset=5]: unknown command 'enable'\r\n. How come we receive malformed message for regular errors? Is Proton Bridge that broken?

[soywod]

May be related: ProtonMail/proton-bridge#451 ProtonMail/proton-bridge#478

[duesee]

And if I still try to enable it, I get once again a MalformedMessage error: 0.1 BAD [Error offset=5]: unknown command 'enable'\r\n.

The message is malformed I would say. But: IMAP is weird.

 0.1 BAD [Error offset=5]: unknown command 'enable'\r\n.

... can be interpreted as ...

Status {
  tag: ...
  code: Some(Other("Error offset=5")),
  // The next ":" is broken
  text: "unknown command `enable`"
}

... or (with a lot goodwill) as ...

Status {
  tag: ...
  code: None,
  text: "[Error offset=5]: unknown command `enable`",
}

See #31. I think the [ and ] should clearly signal that this is a code. But: You could also argue it's a valid message (and imap-codec should consume it)... :-/