When comparing Canary Mail vs Mailspring, the Slant community recommends Canary Mail for most people. In the question“What are the best e-mail clients for macOS?” Canary Mail is ranked 7th while Mailspring is ranked 9th. The most important reason people chose Canary Mail is:
You can assign your default signature to an ALIAS for the same account or create an altogether new one.
Specs
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Pros
Pro Multiple Signatures for Multiple Accounts including ALIASES
You can assign your default signature to an ALIAS for the same account or create an altogether new one.
Pro No personal data stored on servers
No access tokens, passwords, attachments or email itself is stored on Canary servers.
Pro Seamlessly integrates with iOS verion
Gone are the days of manual setup of phone email clients! Canary Mail syncs not just your accounts but all of your settings and even signatures on iCloud.
Pro Local email database is encrypted on disk
Canary stores your local email database encrypted.
Pro Gorgeous and intuitive
Pro Pretty Good Privacy or PGP built-in
Pro Great integration with Gmail
Mailspring has great integration with gmail features and tags.
Pro Neat UI
The UI is very well designed and neat.
Pro Read receipts and link tracking
Activity tracking is built into Mailspring so you get notified as soon as contacts read your messages and can follow up appropriately.
Pro CPU / battery efficient
Mailspring uses a C++ sync engine designed to be as efficient as possible, so you can leave the app running and not see your laptop battery life drain away.
Pro Unified inbox
Using a single inbox for all of your email accounts helps you get more done in less time. Mailspring supports every major mail provider—Gmail, iCloud, Office 365, Outlook.com, Yahoo!, and IMAP/SMTP—so you have a single, streamlined command center for all your messages.
Pro Snoozing support
You can swipe to archive / snooze messages and specify when you'd like them to resurface in your inbox.
Pro Unlimited number of accounts
Only in the paid version though.
Cons
Con Missing mainstream features
No functionality for user-defined Gmail message-tagging, or moving/copying to IMAP folders. Might be acceptable in a free app, but not in one with premium pricing.
Con Buggy
It adds random pins to old emails which then stay on top of the inbox list
Con Poor handling of new emails
You sometimes need to wait very long before your email actually gets delivered.
Con Windows moves randomly
When you create a new email, the new windows is often misplaced so that you have to move it to reach the "Send" button.
Con Poor text editing capabilities
The cursor is laggy so you're better off using keyboard shortcuts.
Con Show NO show
It'll show a new email on a counter, but you're not able to view them.
Con Can't use without creating a Mailspring ID
There is no need to create a third party ID for an email client. What if the Mailspring closes in the future - can't install a previously downloaded Mailspring software any more to continue using it or access your stored emails?
Con Slow updates and bug fixes
It takes months to fix some simple bugs. For example, they can't fix bug with notifications on mac OS from April 2019! Upd: they fixed it after 6-7 months
Con Unstable, have to keep fixing passwords
You have to keep "updating the password" because it continuously finds it hard to sync with multiple Outlook accounts.
Con Pro subscription model
To use some features, like contact profiles and link tracking more than a few times a month, you need to pay for a Pro subscription.
Con No addressbook
Con No way to see messages as plain text
And HTML is only optional.
Con Does not support Microsoft Exchange
Con Very limited user interface
No way to see the messages as a list, no way to rearrange views.
Con No portable windows (.zip) bundle available
Con Does not support POP
Just IMAP.
Con Does not support multi-user installation (Windows)
But instead installs to the user's home directory.
Con UI is sluggish (Windows)
Click and only after a tiny delay (~half second) something happens.