[Enterprise] Nextcloud Mail and RFC2683

[richevanscybermyte]

Issue Description

When fetching email with Nextcloud Mail App, email does not populate.
When syncing mail on the CLI runuser -u www-data -- php occ mail:account:sync 18 -vvv

Works fine with thunderbird.

Nextcloud bug/workaround: https://help.nextcloud.com/t/mail-sync-broken-for-mailbox-argument-exceeds-maximum-length-of-4096-bytes/240891/5

Given that the RFC calls for a larger length, I do not believe this is a Nextcloud Mail issue but a stalwart issue. Stalwart should "allow for a command line of at least 8000 octets" as per the RFC.

Expected Behavior

Mail should populate and occ sync command should function without error

Actual Behavior

runuser -u www-data -- php occ mail:account:sync 18 -vvv
[debug] account is up to date, skipping mailbox sync
[debug] Skipping mailbox sync for 17
[debug] Skipping mailbox sync for 687
[debug] Skipping mailbox sync for 267
[debug] Skipping mailbox sync for 268
[debug] Skipping mailbox sync for 269
[debug] Skipping mailbox sync for 270
[debug] Skipping mailbox sync for 271
[debug] Skipping mailbox sync for 272
[debug] Syncing 20
[debug] Locking mailbox 20 for new messages sync
[debug] Locking mailbox 20 for changed messages sync
[debug] Locking mailbox 20 for vanished messages sync
[debug] Running partial sync for 20
[debug] partial sync 18:Sent Items - get all known UIDs took 0s. 49/50MB memory used
[debug] partial sync 18:Sent Items - get new messages via Horde took 0s. 50/50MB memory used
[debug] partial sync 18:Sent Items - persist new messages took 0s. 50/50MB memory used
[debug] partial sync 18:Sent Items - get changed messages via Horde took 0s. 50/50MB memory used
[debug] partial sync 18:Sent Items - persist changed messages took 0s. 50/50MB memory used
[debug] partial sync 18:Sent Items - get vanished messages via Horde took 0s. 50/50MB memory used
[debug] partial sync 18:Sent Items - delete vanished messages took 0s. 50/50MB memory used
[debug] partial sync 18:Sent Items took 0s
[debug] Unlocking mailbox 20 from vanished messages sync
[debug] Unlocking mailbox 20 from changed messages sync
[debug] Unlocking mailbox 20 from new messages sync
[debug] Skipping mailbox sync for 19
[debug] Syncing 16
[debug] Locking mailbox 16 for new messages sync
[debug] Locking mailbox 16 for changed messages sync
[debug] Locking mailbox 16 for vanished messages sync
[debug] Running partial sync for 16
[debug] partial sync 18:Deleted Items - get all known UIDs took 0s. 50/50MB memory used
[debug] partial sync 18:Deleted Items - get new messages via Horde took 0s. 50/50MB memory used
[debug] partial sync 18:Deleted Items - persist new messages took 0s. 50/50MB memory used
[debug] partial sync 18:Deleted Items - get changed messages via Horde took 0s. 50/50MB memory used
[debug] partial sync 18:Deleted Items - persist changed messages took 0s. 50/50MB memory used
[debug] partial sync 18:Deleted Items - get vanished messages via Horde took 0s. 50/50MB memory used
[debug] partial sync 18:Deleted Items - delete vanished messages took 0s. 50/50MB memory used
[debug] partial sync 18:Deleted Items took 0s
[debug] Unlocking mailbox 16 from vanished messages sync
[debug] Unlocking mailbox 16 from changed messages sync
[debug] Unlocking mailbox 16 from new messages sync
[debug] Syncing 18
[debug] Locking mailbox 18 for new messages sync
[debug] Locking mailbox 18 for changed messages sync
[debug] Locking mailbox 18 for vanished messages sync
[debug] Running partial sync for 18
[debug] partial sync 18:INBOX - get all known UIDs took 0s. 50/51MB memory used
[debug] Unlocking mailbox 18 from vanished messages sync
[debug] Unlocking mailbox 18 from changed messages sync
[debug] Unlocking mailbox 18 from new messages sync

In ImapToDbSynchronizer.php line 282:

[OCA\Mail\Exception\ServiceException]
Sync failed for 18:INBOX: The mail server was unable to parse the contents of the mail message: Argument exceeds maximum length of 4096 bytes.

Exception trace:
at /var/www/html/custom_apps/mail/lib/Service/Sync/ImapToDbSynchronizer.php:282
OCA\Mail\Service\Sync\ImapToDbSynchronizer->sync() at /var/www/html/custom_apps/mail/lib/Service/Sync/ImapToDbSynchronizer.php:133
OCA\Mail\Service\Sync\ImapToDbSynchronizer->syncAccount() at /var/www/html/custom_apps/mail/lib/Command/SyncAccount.php:88
OCA\Mail\Command\SyncAccount->sync() at /var/www/html/custom_apps/mail/lib/Command/SyncAccount.php:72
OCA\Mail\Command\SyncAccount->execute() at /var/www/html/3rdparty/symfony/console/Command/Command.php:326
Symfony\Component\Console\Command\Command->run() at /var/www/html/3rdparty/symfony/console/Application.php:1083
Symfony\Component\Console\Application->doRunCommand() at /var/www/html/3rdparty/symfony/console/Application.php:324
Symfony\Component\Console\Application->doRun() at /var/www/html/3rdparty/symfony/console/Application.php:175
Symfony\Component\Console\Application->run() at /var/www/html/lib/private/Console/Application.php:187
OC\Console\Application->run() at /var/www/html/console.php:87
require_once() at /var/www/html/occ:33

In Socket.php line 4858:

[Horde_Imap_Client_Exception_ServerResponse (6)]
The mail server was unable to parse the contents of the mail message: Argument exceeds maximum length of 4096 bytes.

Exception trace:
at /var/www/html/custom_apps/mail/vendor/bytestream/horde-imap-client/lib/Horde/Imap/Client/Socket.php:4858
Horde_Imap_Client_Socket->_responseCode() at /var/www/html/custom_apps/mail/vendor/bytestream/horde-imap-client/lib/Horde/Imap/Client/Socket.php:4586
Horde_Imap_Client_Socket->_getLine() at /var/www/html/custom_apps/mail/vendor/bytestream/horde-imap-client/lib/Horde/Imap/Client/Socket.php:4319
Horde_Imap_Client_Socket->_sendCmdChunk() at /var/www/html/custom_apps/mail/vendor/bytestream/horde-imap-client/lib/Horde/Imap/Client/Socket.php:4243
Horde_Imap_Client_Socket->_sendCmd() at /var/www/html/custom_apps/mail/vendor/bytestream/horde-imap-client/lib/Horde/Imap/Client/Socket.php:1236
Horde_Imap_Client_Socket->_openMailbox() at /var/www/html/custom_apps/mail/vendor/bytestream/horde-imap-client/lib/Horde/Imap/Client/Base.php:1066
Horde_Imap_Client_Base->openMailbox() at /var/www/html/custom_apps/mail/vendor/bytestream/horde-imap-client/lib/Horde/Imap/Client/Base.php:2247
Horde_Imap_Client_Base->search() at /var/www/html/custom_apps/mail/vendor/bytestream/horde-imap-client/lib/Horde/Imap/Client/Data/Sync.php:186
Horde_Imap_Client_Data_Sync->__construct() at /var/www/html/custom_apps/mail/vendor/bytestream/horde-imap-client/lib/Horde/Imap/Client/Base.php:3643
Horde_Imap_Client_Base->sync() at /var/www/html/custom_apps/mail/lib/IMAP/Sync/Synchronizer.php:99
OCA\Mail\IMAP\Sync\Synchronizer->doCombinedSync() at /var/www/html/custom_apps/mail/lib/IMAP/Sync/Synchronizer.php:69
OCA\Mail\IMAP\Sync\Synchronizer->sync() at /var/www/html/custom_apps/mail/lib/Service/Sync/ImapToDbSynchronizer.php:400
OCA\Mail\Service\Sync\ImapToDbSynchronizer->runPartialSync() at /var/www/html/custom_apps/mail/lib/Service/Sync/ImapToDbSynchronizer.php:263
OCA\Mail\Service\Sync\ImapToDbSynchronizer->sync() at /var/www/html/custom_apps/mail/lib/Service/Sync/ImapToDbSynchronizer.php:133
OCA\Mail\Service\Sync\ImapToDbSynchronizer->syncAccount() at /var/www/html/custom_apps/mail/lib/Command/SyncAccount.php:88
OCA\Mail\Command\SyncAccount->sync() at /var/www/html/custom_apps/mail/lib/Command/SyncAccount.php:72
OCA\Mail\Command\SyncAccount->execute() at /var/www/html/3rdparty/symfony/console/Command/Command.php:326
Symfony\Component\Console\Command\Command->run() at /var/www/html/3rdparty/symfony/console/Application.php:1083
Symfony\Component\Console\Application->doRunCommand() at /var/www/html/3rdparty/symfony/console/Application.php:324
Symfony\Component\Console\Application->doRun() at /var/www/html/3rdparty/symfony/console/Application.php:175
Symfony\Component\Console\Application->run() at /var/www/html/lib/private/Console/Application.php:187
OC\Console\Application->run() at /var/www/html/console.php:87
require_once() at /var/www/html/occ:33

Reproduction Steps

Configure Nextcloud Mail app to use Stalwart via IMAP

Relevant Log Output

2026-03-19T23:50:15Z DEBUG IMAP error occurred (imap.error) listenerId = "imaptls", localPort = 993, remoteIp = x.x.x.x, remotePort = 59351, details = "Argument exceeds maximum length of 4096 bytes.", id = "5", type = "BAD", code = "PARSE"
2026-03-19T23:50:15Z TRACE Raw IMAP output sent (imap.raw-output) listenerId = "imaptls", localPort = 993, remoteIp = x.x.x.x, remotePort = 59351, size = 62, contents = "5 BAD [PARSE] Argument exceeds maximum length of 4096 bytes.\r\n"

Stalwart Version

v0.15.x

Installation Method

Binary (Linux)

Database Backend

RocksDB

Blob Storage

S3-compatible

Search Engine

Internal

Directory Backend

LDAP

Additional Context

No response

I acknowledge that:

• I have reviewed the documentation and FAQ and confirm that my issue is NOT addressed there.
• I have searched the Stalwart repository (both open and closed Discussions and Issues) and confirm this is not a duplicate.
• I have set the logging level to trace and included relevant log output if applicable.
• I agree to follow the project's Code of Conduct.

[mdecimus]

The Nextcloud link you included times out, make sure they're not passing the entire email as an argument without using literals. In any case, this has been fixed in the v0.16 dev branch.

[richevanscybermyte]

Thank you. Yeah, I have a trace on what was passed and it looks like it passed the standard QRESYNC command then all the message UID/Ranges, that is when the actual error occurred.
Yes, I see the fix was added, thank you. Do you have a timeline for 16? You guys are quick on your releases but it is good to know when I can remove the work around.
Also, will you be back porting to 15? Just for the people that are not ready to update due to the changes in 16.
Thank you and your team!

[mdecimus]

Although v0.16 is close to completion, we still need to rewrite the webadmin and CLI to use the new JMAP API, so it might take a few weeks until the release. If you need this fix urgently I recommend that you apply this commit to the main branch and recompile Stalwart locally. This is because there are no plans to release another v0.15 minor release unless there is a critical bug.

[richevanscybermyte]

Makes sense, I have a workaround in place right now but gets blown away when I update my tenants mail app. They begin to have issues accessing mail, essentially they become down on mail. I am not sure what your critical bugs are categorized as but down on mail when this app is a mailserver seems pretty high on the list.