I have tried many different E-Mail services. Gmail, Hotmail, Outlook.com, iCloud and briefly Protonmail. But all of them seemed lacking. Then I switched to Office 365.
Mainly my complaints with the free offerings were the ability to actually sync well between my devices. I have a mix of iOS, Android, Windows and Mac OS clients, and none of them played well with all of the different mobile operating systems and Microsoft Outlook. Almost all of them didn't play nice with at least one client, and required special apps or special plugins for Outlook
I also had a hard time finding good usernames. I have a short name, so it's ALWAYS taken and I have to settle for something stupid like: [email protected] (I'm sure thats someones real E-Mail address, so say hi to them maybe)
I decided to purchase my own domain name, and look into either self-hosting an E-Mail server or use a cloud service. Self hosting seemed like a lot of work with needing to obtain a static IP with good reputation (So most VPS's are out of the question) and if it went down, I would be missing emails... No fun.
In the end I decided on Office 365 Business Essentials with is $5 a month, paired with Azure Information Protection Plan 1 which is a $2 addon. This gives me pretty much full hosted Exchange with E-Mail encryption for $7 a month. I have 4 different domains added, and I use it as my primary SMTP host too for notification emails from all my services.
The sync works perfectly with everything, and obviously works flawlessly with Outlook.
You get a 50GB Mailbox, and shared mailboxes are 50GB too, and you can just keep making them... (So, unlimited?)
You get 1TB of OneDrive, and 1TB of SharePoint Online which is almost useless as their API is throttled to hell and back, but it does let you share large files without using your own bandwidth though. Its a shame there is still a 15GB filesize limit though.
If you are looking for a better email solution, I would suggest you look into Office 365.