Gmailでの手動IMAPコピー日付の修正

Manual IMAP copy to Gmail involves adding both a source IMAP account and the Gmail account to an メールクライアント (Outlook, Thunderbird, or Apple Mail) and copying messages between them. When the メールクライアント uploads messages to Gmail via IMAP APPEND, Gmail records the upload timestamp as the message's INTERNALDATE. The メールクライアント does not pass the original INTERNALDATE from ソースサーバー because most clients do not support this during copy operations.

Gmail's IMAP handling introduces an additional complication. Gmail processes uploaded messages through its own pipeline, adding a Receivedヘッダー that contains the Gmail IMAP gateway timestamp. This Receivedヘッダー becomes the topmost entry in the ヘッダーチェーン. While Gmail's Webインターフェース uses the Dateヘッダー for display (potentially showing 正しい日付s), every IMAP client that subsequently connects to the Gmail account reads the corrupted INTERNALDATE.

Users who manually copy emails to Gmail often do so when consolidating multiple email accounts or when moving from a less common email provider that is not supported by standard migration tools. The simplicity of drag-and-drop in an メールクライアント masks the underlying 日付の破損 that occurs at the IMAP protocol level. The problem becomes apparent when the ユーザー checks their Gmail account from a different client or when an IMAP-connected バックアップ tool archives the 間違った日付s.

In Gmail, the impact follows the familiar split: the Webインターフェース may show 正しい日付s (from the Dateヘッダー) while IMAP clients show the copy date (from the INTERNALDATE). Users who access Gmail only through the web browser may not notice the issue. Users who use Outlook, Apple Mail, or Thunderbird connected to Gmail via IMAP see the copy date for all manually transferred messages.

Gmail's label system preserves the labels applied during the copy, but the sorting within labels uses the INTERNALDATE when accessed via IMAP. IMAP clients that sort by server date display the copied messages out of their original chronological order. Google Takeout exports and third-party バックアップ tools record the copy date as the message date, creating permanent inaccuracies in exported archives. For ユーザー who manually consolidated years of email from multiple accounts into Gmail, the 日付の破損 can affect a significant portion of their entire email history.