When comparing Kontact vs Mailspring, the Slant community recommends Mailspring for most people. In the question“What are the best native e-mail clients for Linux?” Mailspring is ranked 6th while Kontact is ranked 8th. The most important reason people chose Mailspring is:
The UI is very well designed and neat.
Ranked in these QuestionsQuestion Ranking
Pro Integrated calendaring
The integrated calendaring support means that incoming invitations can be accepted with a click and they get put into your calendar automatically.
Pro Multi-account, multi-identity
Supports both multiple accounts from different servers / services simultaneously (both inbound and sending) as well as multiple identities. Incoming accounts have a default identity and it switches automatically to the correct identity depending on the mail folder you are in.
Fully supports PGP and S-MIME with built-in certificate management. Encrypt, sign and verify emails easily and securely.
Pro Contacts, Todos, Notes, Journals, Feeds ....
There are numerous components that come with Kontact that augment the mail experience including contact management, todo lists, note takers and an RSS feed reader, among others.
Pro Supports multiple groupware servers and services
Besides being able to connect to any IMAP, POP3 and SMTP server, you can also connect your Google and Facebook accounts and access Kolab and Tine servers natively.
Pro Continuous, active development
Kontact has been actively developed for over a decade, with components such as the mail and calender going back even further. Development continues to this day with an active and responsive open source community made up of both volunteers and paid developers behind it.
Pro Solid offline IMAP
IMAP support is a strong point for Kontact, with offline mail and sync being transparent and automatic. Read and create mails on the go and everything syncs quickly and reliably when network connectivity is available.
Pro Built-in search
Searching for emails is simple with the search box in the main window which can scan through email bodies, email flags, recipients, etc. Lightening fast in recent versions.
Pro Spam, scam and adblock features
Supports spam filtering, scam detection and adblock for HTML mails.
Pro Keyboard friendly
Can be driven almost entirely from the keyboard. Moving an email, for instance, is a simple matter of hitting 'm' and then typing to filter through the list of folders that appears.
Pro Plain text and HTML mail editing
Provides support for rich-text (HTML) mail editing, but kindly defaults to plain text. Also supports viewing HTML emails with several security features built-in.
Works on Linux/BSD (all desktop environments and window managers), Windows and Mac.
Has flexible and powerful options, from "traditional" conversation-style threading to organizing by date, by senders and receivers, .... paired with "keep replies in same folder" it is easy to track conversations over time.
Supports client and server-side filtering of mails by subject, recipients, mailing list, body text, etc.
Pro Very flexible user interface
You can make the Kontact UI look and function how you want. You can re-arrange the main interface, as well as make the list of mails show or hide almost anything you could need.
Pro Professional support
For enterprise deployments, having commercial support can be a big plus. Companies such as Kolab Systems provide professional support and consulting services for Kontact.
Pro Integration with kde plasma
Based on qt, and part of plasma suite, it integrates well with other KDE apps like kwallet, calendar, etc.
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 Crashes frequently
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.