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lieer vs OfflineIMAP: catalog facts
lieer	OfflineIMAP
Free Free and open source under the GPL-3.0 or later.	Free Free and open source under the GPL.
macOS, Linux, Command line	macOS, Linux, Command line
Two-way sync between Gmail labels and notmuch tags Keeps a full local maildir copy of the mailbox	Two-way sync into plain Maildir, which any local mail client can read Per-folder rules and filters for what gets mirrored
Only works with Gmail accounts Requires notmuch and command-line setup	Python performance is poor on very large mailboxes Configuration is a hand-written file with many options
Downloadable app	Downloadable app
Open source	Open source
License: GPL-3.0-or-later	License: GPL-2.0
Account needed	Not stated if an account is needed
Works offline	Not stated if it works offline
Official website Full listing and sources Checked October 1, 2026	Official website Full listing and sources Checked September 22, 2026

Catalog facts only. Anything “not stated” is unconfirmed. Check full listings for details.