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Boomerang for Gmail vs Mailbutler: catalog facts
Boomerang for Gmail	Mailbutler
Free Can be added to Gmail for free; the homepage does not list paid tiers.	Paid Subscription service with a 14-day free trial.
Browser extension	macOS, Browser extension
Send-later scheduling inside Gmail Email reminders	Works inside Apple Mail and Gmail Mail merge with scheduled sending
Only works with Gmail and Google Workspace Requires granting access to your Gmail account	Email tracking reveals recipient activity, which some recipients object to Requires a subscription after the trial
Browser extension	Downloadable app, Browser extension
Closed source	Closed source
License not stated	License not stated
Account needed	Account needed
Needs internet	Not stated if it works offline
Official website Full listing and sources Checked September 23, 2026	Official website Full listing and sources Checked September 23, 2026

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