2048208 - Thunderbird issues IMAP APPEND with UTF8 flag but UTF8=APPEND not advertised

Status: RESOLVED MOVED

(MailNews Core :: Networking: IMAP, defect)

Description

[wullinger]

Steps to reproduce:

• Install a new IMAP Server with cyrus imapd 3.12.1.
• Create an account with a mailbox on the server in Thunderbird
• Copy a message from another IMAP account to a mailbox on the new account

Actual results:

The copy operation fails with

BAD Invalid argument in Append command

Thunderbird issues the IMAP commands

ENABLE UTF8=ACCEPT
append "INBOX" (<flags>) "17-Jun-2026 12:38:33 +0200" UTF8 (~<literal>).

The UTF8 flag to APPEND is rejected by cyrus imapd. Following RFC5738, this seems to be correct. The server advertises UTF8=ACCEPT and not UTF8=APPEND (nor UTF8=ONLY or UTF8=ALL).

Expected results:

The message is copied to the destination folder

Comment 1

[wullinger]

For cyrus imapd a workaround is to set

suppress_capabilities: UTF8=ACCEPT
in imapd.conf to avoid the IMAP server advertising UTF8 support.

Comment 2

[Magnus Melin [:mkmelin]]

Please provide an IMAP log. See https://wiki.mozilla.org/MailNews:Logging

Comment 3

[wullinger]

Attachment: MOZ_LOG=IMAP:4 when trying to copy a file from a local folder to cyrus imapd 3.12.1

Comment 4

[Magnus Melin [:mkmelin]]

Well, UTF8=APPEND is from an outdated spec. See https://datatracker.ietf.org/doc/html/rfc6855.html#section-9

Thunderbird could avoid doing that if there are no non-ascii chars I suppose.

Comment 5

[wullinger]

(In reply to Magnus Melin [:mkmelin] from comment #4)

Well, UTF8=APPEND is from an outdated spec. See https://datatracker.ietf.org/doc/html/rfc6855.html#section-9

Thanks for the pointer. Mention of UTF8=APPEND is by me. Cyrus never advertises it.

It advertises UTF8=ACCEPT, but it seems that this is interpreted in the sense of RFC5738, not RFC6855.
This probably warrants a bug report against cyrus.

Comment 6

[wullinger]

Cross-Reference to the issue with Cyrus Imapd: https://github.com/cyrusimap/cyrus-imapd/issues/6078

Comment 7

[Magnus Melin [:mkmelin]]

The Cyrus bug has been fixed

Comment 8

[Wayne Mery (:wsmwk)]

(In reply to Magnus Melin [:mkmelin] from comment #7)

The Cyrus bug has been fixed

Patch dated June 23.

But not yet shipped afaict. https://github.com/cyrusimap/cyrus-imapd/releases shows last release as cyrus-imapd-3.12.2, which was March 29, 2026.