fix(send): skip IMAP APPEND when server already saved sent message

[ChristophWurst]

Some mail servers (e.g. Microsoft Exchange/Office 365) automatically save a copy of sent messages to the Sent folder upon SMTP submission. When Nextcloud Mail also does an IMAP APPEND, the user ends up with duplicates.

After SMTP delivery succeeds, search the Sent mailbox for the outgoing message's Message-ID header. If the server already saved it, skip the APPEND. If the IMAP search fails for any reason, fall through and APPEND as normal (safe degradation).

AI-assisted: Claude Code (claude-sonnet-4-6)

Summary by CodeRabbit

• Bug Fixes

  • Prevented duplicate saves to the Sent folder when the mail server has already stored the sent message (handler now skips redundant appends).

• Tests

  • Added unit and integration tests to verify skipping behavior and proper fallback when mailbox existence checks fail.

[ChristophWurst]

/backport to stable5.8

[ChristophWurst]

/backport to stable5.7

[ChristophWurst]

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ℹ️ Recent review info

⚙️ Run configuration

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Review profile: CHILL

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Run ID: e6a1d310-11ca-47a6-b9b5-ff5ab967d2a8

📥 Commits

Reviewing files that changed from the base of the PR and between 09a5b4c and 8475dea.

📒 Files selected for processing (1)

• lib/Send/CopySentMessageHandler.php

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📝 Walkthrough

Walkthrough

Adds Message-ID-based duplicate detection: MessageMapper gains existsInMailboxByMessageId(...), CopySentMessageHandler uses it to skip APPEND when the Sent mailbox already contains the message, and unit + integration tests cover skip and fallback paths.

Changes

Skip Append When Server Already Saves Message

Layer / File(s)	Summary
Message-ID existence lookup in MessageMapper lib/IMAP/MessageMapper.php	New public method existsInMailboxByMessageId() performs IMAP SEARCH for messages matching a Message-ID header and returns whether any matching message exists in the mailbox.
CopySentMessageHandler server-save detection and skip lib/Send/CopySentMessageHandler.php	Imports OCA\Mail\Db\Mailbox, adds private helper isAlreadySavedByServer() to extract Message-ID and consult MessageMapper, and updates process() to mark message STATUS_PROCESSED and skip append when the server already saved it.
Unit tests for skip and fallback paths tests/Unit/Send/CopySendMessageHandlerTest.php	Adds tests that verify the handler skips append when Message-ID exists and falls back to append when the IMAP search throws, asserting status changes and next-handler invocation.
Integration test for server pre-save scenario tests/Integration/Service/MailTransmissionIntegrationTest.php	End-to-end test simulates a pre-saved Sent message with a generated Message-ID, invokes the handler, and asserts the Sent mailbox remains with a single message (no duplicate append).

sequenceDiagram
  participant Handler as CopySentMessageHandler
  participant Helper as isAlreadySavedByServer
  participant Mapper as MessageMapper
  participant IMAP as IMAP Server
  Handler->>Helper: extract Message-ID, check server state
  Helper->>Mapper: existsInMailboxByMessageId(messageId, mailbox)
  Mapper->>IMAP: SEARCH HEADER Message-ID "messageId"
  IMAP-->>Mapper: search results (count)
  Mapper-->>Helper: exists? (true/false)
  alt Server already saved
    Helper-->>Handler: true
    Handler->>Handler: set STATUS_PROCESSED, skip append
  else Need to append
    Helper-->>Handler: false
    Handler->>Handler: proceed with normal save flow
  end

Loading

🎯 3 (Moderate) | ⏱️ ~20 minutes

🐰 A tiny hop, a message id,
The server saved it, swift and sly,
Mapper peeks and gives a nod,
Handler skips the extra plod,
Sent folder stays neat — hop bye-bye! ✨

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 16.67% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title accurately and specifically describes the main change: adding logic to skip IMAP APPEND when a mail server has already automatically saved the sent message, which is the core problem being solved across the modified files.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch fix/avoid-duplicate-sent

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Actionable comments posted: 1

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Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Inline comments:
In `@lib/Send/CopySentMessageHandler.php`:
- Around line 33-35: The Message-ID regex currently inspects the entire MIME
payload ($rawMessage) in CopySentMessageHandler, which can match a
Message-ID-like line in the body; instead extract the header block only
(everything before the first blank line) and run the Message-ID match against
that header string. Locate the code using $rawMessage (the block with
preg_match('/^Message-ID:.../im', $rawMessage, $m)), split or capture headers
(e.g. split on the first double newline using preg_split or preg_match with
'/\A(.*?)(?:\r?\n){2}/s') to get $headers, then apply the existing
'/^Message-ID:\s*(<[^>]+>)/im' regex to $headers and return false if not found.

🪄 Autofix (Beta)

Fix all unresolved CodeRabbit comments on this PR:

• Push a commit to this branch (recommended)
• Create a new PR with the fixes

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ℹ️ Review info

⚙️ Run configuration

Configuration used: Path: .coderabbit.yaml

Review profile: CHILL

Plan: Pro Plus

Run ID: a106c86d-862d-4aca-9cb9-d638dc3622ed

📥 Commits

Reviewing files that changed from the base of the PR and between 8cb01dc and 09a5b4c.

📒 Files selected for processing (4)

• lib/IMAP/MessageMapper.php
• lib/Send/CopySentMessageHandler.php
• tests/Integration/Service/MailTransmissionIntegrationTest.php
• tests/Unit/Send/CopySendMessageHandlerTest.php

[ChristophWurst]

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