Foundry376/Mailspring · error

A label is required.

Error message

A label is required.

What it means

Validation guard in the MailRuleProcessor's applyLabel action handler. It fires when a mail rule's 'apply label' action has an empty/missing value — the rule was saved without a label id, or the stored label id is an empty string.

Source

Thrown at app/src/mail-rules-processor.ts:108

  changeFolder: async (message, thread, value) => {
    if (!value) {
      throw new Error('A folder is required.');
    }
    const folder = CategoryStore.byId(thread.accountId, value);
    if (!folder || !(folder instanceof Folder)) {
      throw new Error('The folder could not be found.');
    }
    return new ChangeFolderTask({
      folder: folder,
      threads: [thread],
      source: 'Mail Rules',
    });
  },

  applyLabel: async (message, thread, value) => {
    if (!value) {
      throw new Error('A label is required.');
    }
    const label = CategoryStore.byId(thread.accountId, value);
    if (!label || !(label instanceof Label)) {
      throw new Error('The label could not be found.');
    }
    return new ChangeLabelsTask({
      labelsToAdd: [label],
      labelsToRemove: [],
      threads: [thread],
      source: 'Mail Rules',
    });
  },

  archive: (message, thread) => {
    const inbox = CategoryStore.getInboxCategory(thread.accountId);
    if (!inbox) {
      throw new Error('Could not find `inbox` label');
    }

View on GitHub (pinned to 648c685d60)

Solutions

1. Open Preferences > Mail Rules and edit the rule so the 'apply label' action has a label selected
2. Delete or disable the malformed rule if it is no longer needed
3. If programmatically creating rules, ensure each applyLabel action includes a valid label id

When it happens

Trigger: Thrown at app/src/mail-rules-processor.ts:108 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of Foundry376/Mailspring@648c685d60 (2026-09-03). Data as JSON: /api/errors/f21703424596fc87. Report an issue: GitHub.