IMAP error "Too long argument" when copy/moving/deleting more than 10,000 messages (missing UID range compression)

[lvarnava]

Hi @kimusan.

When performing bulk operations (such as cope,moving or deleting more than ~10,000 messages at once) in Tachyon v4.5.0, the operation fails with a CantMoveMessage[204] error caused by the IMAP server rejecting the command with Too long argument.
Root Cause:
In MailSo\Imap\Commands\Messages (and ImapClient), Tachyon sends the full list of message UIDs as a plain comma-separated string (e.g., UID MOVE 89015,89014,89013,...,72878 "Trash") instead of compressing consecutive UIDs into IMAP sequence ranges (e.g., 72878:89015).
When selecting ~11,000+ messages, the command line length exceeds the default 64 KB IMAP (dovecot) command limit on standard servers like Dovecot (imap_max_line_length), resulting in a BAD response.

Logs:

IMAP[WARNING]: MailSo\Imap\Exceptions\NegativeResponseException: Error in IMAP command UID STORE: Too long argument in /usr/share/tachyon/tachyon/v/4.5.0/app/libraries/MailSo/Imap/ResponseCollection.php:46
IMAP[INFO]: > TAG4 UID MOVE 89015,89014,89013,...,72878 "Trash"
IMAP[INFO]: < TAG4 BAD Error in IMAP command UID MOVE: Too long argument
SERVICE[WARNING]: CantMoveMessage[204]

Suggested Fix:

1. Compress consecutive UIDs into IMAP ranges (start:end) before sending commands like UID STORE, UID MOVE, UID COPY, etc.
2. Optionally, split large UID lists into smaller chunks/batches if the resulting command string still exceeds a safe length threshold (e.g., 8–16 KB).

The AI ​​helped me create the query, so I'm not sure how correct the suggested solutions are.
For now, I've set the value 512k here:

protocol imap {
  imap_max_line_length = 512k
}

As far as I understand, increasing this value entails the risk of increased RAM consumption and DoS attacks.

doveconf -d| grep imap_max_line_length
imap_max_line_length = 64 k

Thank you!

[kimusan]

Thanks, this was a good find. The diagnosis is right: Tachyon already merged runs of UIDs into ranges, but only when they came in ascending order, and the message list sends them newest first, so nothing merged. That is why your log shows every UID on its own.

The fix sorts the UIDs before merging them, so a whole folder goes out as a single range like 72878:89015. If the selection is spread out with big gaps, it is split over several commands of at most 8000 characters each, which RFC 7162 recommends. I tested it against Dovecot with its default 64k limit and 14,500 messages, and moves, copies and deletes all work.

It is in 4.6.0, so you can put imap_max_line_length back to 64k once you have updated.

[lvarnava]

Tachyon 4.6.0.
Thank you @kimusan.
imap_max_line_length = 64 k
16,000+ emails deletes.