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Aerion vs eM Client: catalog facts
Aerion	eM Client
Free Free and open source under the Apache 2.0 licence.	Freemium Free licence for personal, non-commercial use with up to two accounts; Personal from…
Windows, macOS, Linux	Windows, macOS, Android, iOS
Built with Wails instead of Electron for lower resource use Direct IMAP and SMTP connection with mail stored locally	Handles Gmail, Microsoft 365, Outlook, Exchange and plain IMAP without plugins Email, calendar, tasks, contacts, notes and chat in one polished window
Young project with a smaller feature set than established clients Tracking protection is described as basic	No Linux version The free licence is capped at two accounts and forbids any commercial use
Downloadable app	Downloadable app
Open source	Closed source
License: Apache-2.0	License not stated
No account needed	Account needed
Not stated if it works offline	Works offline
Official website Full listing and sources Checked October 1, 2026	Official website Full listing and sources Checked September 20, 2026

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