Outgoing Undo for Mailspring

Restores Mailspring's built-in Sending soon… toast in the main window when sending from a separate composer window. The existing countdown, Undo, and Send now instead controls remain Mailspring's own controls.

Install

1. Download mailspring-outgoing-undo.zip from the latest release.
2. Extract the ZIP. Copy the mailspring-outgoing-undo folder into Mailspring's packages directory (create packages if it doesn't exist).
3. Save open drafts and restart Mailspring.
4. Enable a nonzero Undo Send delay in Mailspring's sending preferences.

Typical package directories:

Platform	Directory
macOS	~/Library/Application Support/Mailspring/packages/
Linux	~/.config/Mailspring/packages/
Windows	%APPDATA%\Mailspring\packages\

Linux installations using a custom XDG_CONFIG_HOME, Snap, or a custom config directory may use a different location. Developer > Show Mailsync Logs opens the configuration directory; create/use its packages subdirectory. The installed folder must contain package.json directly, without an extra nested folder. No npm install or build is needed.

To remove it, delete mailspring-outgoing-undo from the packages directory and restart Mailspring.

Why it works

In Mailspring 1.25.0, SyncbackMetadataTask calculates canBeUndone in its constructor. The cross-window action bridge reconstructs an empty task and then fills it with fromJSON, leaving that flag false even when undoValue is present. UndoRedoStore therefore ignores the task and shows no toast.

This plugin wraps that task's fromJSON in the main window to recalculate the flag after loading the data. It restores the original method when disabled. It adds no sending mechanism, network access, or dependencies.

Compatibility and validation

The implementation was checked against Mailspring 1.25.0 (commit add26bb9) on macOS. It uses an internal API; other versions may require changes. Windows and Linux have not been tested.

The isolated regression check passes. A separate check against extracted Mailspring 1.25.0 source reproduced the missing flag and verified that the plugin lets the native undo store register the task and queue cancellation metadata. Live email sending and clicking the toast have not been tested.

The plugin uses the existing undo-send delay. It cannot recall a message after delivery or provide an undo window when the delay is disabled.

Check

Run node test.js (or npm test) for the isolated regression check.

For a live check, send a test message to yourself from a new compose window, then click Undo in the main window before the countdown ends. Confirm it remains a draft. Also check a normal inline reply and Send now instead. Automated checks do not send email.

Mailspring's package installation convention is documented in the official plugin starter.

Feedback

Open an issue with your Mailspring version, operating system, Undo Send delay, and whether the message was sent inline or from a separate window. Do not include private message content or account credentials.

License

MIT. This is an unofficial community plugin.