The as_bytes method of an email message can fold headers improperly.

[msapiro]

Bug report

Bug description:

This code

import email
msg = email.message_from_bytes(b"""To: user@example.com
From: "Txxxxxx Mxxxxxxx de Vxxxxxx, Fxxxxxxxx" <fxxxxxxxx.txxxxxx@subd.example.net>

body
""")

creates a message object which when flattened as bytes erroneously folds the long From: header following the comma inside the quoted string.

msg.as_bytes()
b'To: user@example.com\nFrom: "Txxxxxx Mxxxxxxx de Vxxxxxx,\n Fxxxxxxxx" <fxxxxxxxx.txxxxxx@subd.example.net>\n\nbody\n'

CPython versions tested on:

3.9, 3.11

Operating systems tested on:

Linux

[RanKKI]

If I understand RFC 5322 3.2.4 correctly:

Since a quoted-string is allowed to contain FWS, folding is permitted.

Therefore, I don't think it's a bug, as it should not exceed 78 characters.

[msapiro]

I agree that the current behavior is RFC 5322 compliant and I'm closing this.