When comparing Mozilla Thunderbird vs Mailspring, the Slant community recommends Mozilla Thunderbird for most people. In the question“What are the best e-mail clients for Windows?” Mozilla Thunderbird is ranked 1st while Mailspring is ranked 4th.
Ranked in these QuestionsQuestion Ranking
Pro Free (as in freedom and beer)
Pro Lightning Calendar and Address Book integration
Pro Available on Linux, OS X and Windows
Pro Good filtering system
Mozilla Thunderbird offers a flexible filtering system with the ability to set flags and read/unread, as well as sort/assign to new mail directories. There are also numerous plugins available to assist in the filtering.
Pro Very reliable
Version after version, Mozilla Thunderbird works as expected.
Pro Consistent and involving a moderate learning curve
The app design of Mozilla Thunderbird has not changed significantly since its beginning, making its learning curve almost non-existent.
Pro Large assortment of plugins available
Mozilla Thunderbird offers a huge amount of extensions to expand the usability and options of the client.
Pro Tabs for navigation
Pro Send large files easy
Install pCloud plugin for Thunderbird and your files (upto 20 GB free storage included) will be received as download links
Pro Neat UI
The UI is very well designed and neat.
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 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 Great integration with Gmail
Mailspring has great integration with gmail features and tags.
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.
Con Terrible integration with macOS
Simple things - drag/dropping pictures doesn't work, for instance.
Con Development slowed to only focus on stability and security
Mozilla Thunderbird has slowed down its development of features to only focus resources on security and stability.
Con Subject lines can (temporarily) disappear from the list
This is sporadic behavior.
Con Serious bugs
Clicking on a subject line can bring up the wrong email.
Con Outdated interface
Thunderbird's interface is very outdated and unpleasant. It feels more like a Windows XP application than like a modern MacOS one.
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 No addressbook
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 portable windows (.zip) bundle available
Con Does not support POP
Con Very limited user interface
No way to see the messages as a list, no way to rearrange views.
Con No way to see messages as plain text
And HTML is only optional.
Con UI is sluggish (Windows)
Click and only after a tiny delay (~half second) something happens.
Con Does not support multi-user installation (Windows)
But instead installs to the user's home directory.