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