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

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