When comparing Microsoft Outlook vs ProtonMail, the Slant community recommends Microsoft Outlook for most people. In the question“What are the best e-mail clients for Windows?” Microsoft Outlook is ranked 7th while ProtonMail is ranked 10th. The most important reason people chose Microsoft Outlook is:
The calendar includes agenda, day, and three-day views.
Specs
Ranked in these QuestionsQuestion Ranking
Pros
Pro Good built-in calendar
The calendar includes agenda, day, and three-day views.

Pro Integration with calendar and tasks
Quick conversion of a received email to a task with the deadline.
Pro Fun to use
clean and smooth experience, very nice and i like it.
Pro Smart lookup
Smart lookup is a feature where the Bing search engine is bundled in the app to allow users to automatically search for relevant websites, information and images based on the word highlighted by users, without need to open external browsers. The results will be shown on the right pane of the window.
Pro Priority messages
Microsoft Outlook comes with feature called "Clutter" to filter out incoming email based on the priority of the message set by user. User will be alerted when the high-priority message is incoming, whereas the low-priority message will be put in a separate folder.
Pro Attach files from cloud
Microsoft Outlook allow users to directly attach an attachment directly from cloud services without need to download an entire file before attach to the intended e-mail.
Pro VBA macros
Pro Conditional formatting
Pro Cloud
can attach files and use cloud, very good.
Pro Built-in end-to-end encryption
Pro No personal information needed
To create an account you don't need to give any personal information, just choose username, domain, and password. Even the recovery email address is optional.
Pro Privacy respecting
User data is protected by strict privacy laws because all servers are located in Switzerland.
Pro Open Source
Pro Mobile apps
Apps for Android and iOS available.
Cons
Con It's from Microsoft
Con Rather buggy
Con Crashes frequently
The only issue with Outlook 2017 is that when the Mail folder increases in size, it sometimes crashes for no reason it, causing loss of data.
Con Categorize email IMAP not good
Con Frustrating user experience
The "Clean Interface" approach means that normal and necessary user interface elements have been removed, such as certain scroll bars, and even the "replied to" indicator. This program becomes more frustrating with each new update.
Con No unique Inbox / global folders
Con No portable bundle available
Con No aliases
Outlook does not support email aliases other then outlook aliases
Con The UI is outdated
Con Only available for Windows
Con Javascript-intensive Webmail
Free accounts are required to use Javascript webmail and encryption is done in the browser. Javascript cryptography is harmful for security and should not be used.
Con Encryption Keys are stored server-side
The keys are generated during account creation. Using your existing keys is prohibited and ProtonMail must store and control the private keys. Encryption cannot be secure unless the user controls the private keys.
Con Still lacks some useful features
At the moment, there is no calendar feature and contact management is quite poor. They will, however, start to work on it.
Con Ties to US Investors
ProtonMail takes money from US Investors
Con No IMAP and SMTP support for basic accounts
Basic accounts are restricted to the Protonmail web client. Support for IMAP and SMTP is available with a paid subscription only, and as such with basic accounts it is not possible to send and receive email with external applications.
Con Overly expensive for desktop support
Con Requires phone number for login
If you sign up over Tor or a VPN, it will require email or phone number verification. Email verification is disabled if you use an email that isn't from Google or Outlook.
Con Not fully Open Source
