When comparing Evolution vs Kontact, the Slant community recommends Evolution for most people. In the question“What are the best native e-mail clients for Linux?” Evolution is ranked 5th while Kontact is ranked 7th. The most important reason people chose Evolution is:
Evolution is one of the few Linux desktop e-mail clients that's supports exchange servers.
Specs
Ranked in these QuestionsQuestion Ranking
Pros
Pro Supports exchange servers
Evolution is one of the few Linux desktop e-mail clients that's supports exchange servers.
Pro Great integration with Gnome environment
Pro Manages contacts, tasks, calendar and memos as well
Pro Excellent GPG support
The integration with GPG is excellent. You can sign, encrypt, decrypt, authenticate and verify GPG signatures and GPG signed/encrypted email messages. All of that is just a setting away.
Pro Good support for Google's services
Pro Clean interface with 2 layout variants
Going to View > Preview has the option of switching between "Classical View" and "Vertical View".
Pro HTML rendering is great
Of the many email clients available on GNU/Linux, Evolution has the best HTML renderer. It renders HTML and the entire email content exactly like it would appear on a full blown web browser. Not many email clients are capable of doing that.

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.

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 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 Encryption
Fully supports PGP and S-MIME with built-in certificate management. Encrypt, sign and verify emails easily and securely.

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 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.

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 Integration with kde plasma
Based on qt, and part of plasma suite, it integrates well with other KDE apps like kwallet, calendar, etc.

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 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 Cross-platform
Works on Linux/BSD (all desktop environments and window managers), Windows and Mac.

Pro Threading
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.

Pro Filtering
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.
Cons
Con Can't choose different settings for each mail account
Settings have to applied to all mail accounts.
Con Limited configuration options
Cannot format date as preferred.
Con RAM heavy
Very heavy on RAM usage.
Con Poor integration in any non-GNOME desktop
It is written with GNOME in mind.
Con No configuration messages
Although base functions like bullets, numbered, or pre-formatted text are possible, you can't select or set the font for your messages. Not even serif or sans serif. Which is a bit spartan TBH.
Con Can be wobbly with EWS
Don't be surprised if you have to reboot it a couple of times during a working day, because error messages are piling up (e.g. connection lost, can't sync, can't store appointment, read only). Then again, is this Evolution, or what it connects to? And since such an occasional reboot is dwarfed by the fact that MS365 seems to make full IMAP/ SMTP access (close to) impossible (nice meeting invite, THX, but when is it?), just reboot and get some work done...
Con Only available on Linux
If you have to switch to another platform for whatever reason, you will need to search for a different email client.
Con Crashes frequently
Con Akonadi
