Why Office 365 Exchange Online is better than POP3 Mail Hosting? 

Office 365 / Exchange Online (like IMAP Mail Hosting)	POP3 Mail Hosting
Secure connection – authentications are over secured channels.	Unsecure connection – authentications are done in plain text, which is subceptible to man-in-the-middle attack, not always from outside the network, but sometimes inside as well.
No duplicate mail issues – mailbox contents are sychronized with server mailbox.	Duplicate mails when mail client loses information on last email downloaded.
Synchronize your mailbox across multiple connected device.	Emails sent or entries added on one device may not be on another, eg. messages sent from PC will not be accessible on mobile device.
Push mail ensure mails coming in are immediate to all connected nodes.	Emails are received on scheduled timing indicated on mail clients.
25Gb of storage per mailbox ensure minimal issue on mail quota.	Mailbox sizes are usually smaller, shared between user accounts with higher cost for bigger disk space.
For E2 plan, comes with license to use desktop version of Office Professional Plus 2013 (on up to 5 devices) alleviating the need to buy additional licenses for each desktop/device that is purchased. For the other Office 365 plans, you can still view & edit Words, Excel, Powerpoint files via web-based.	No option for office apps on any traditional mail hosting plans.
Flexibility to access your mails & calendar from multiple devices like PC, Mac, web, iPhones, or other mobile devices with similar & familiar view & interface.	Each device operates separately. Difficult to sync across all devices.
Global address list allows you to access centralized, frequently used contacts on the go.	Each contact list on each device operates separately from the others.
Support for multiple domains for a single fee.	Each additional domain will have additional costs.
Access your calendar on the go. All edits & entries are sychronized & similiar	Individual calendar on each device. New entries are not updated on all nodes.
Share calendar with the ability to control amount of information accessible.	No calendar sharing support.
Sent Items, Drafts, Deleted Items are synchronized & whatever sent, created or deleted is available across all devices.	Each clients operates separately & sent emails are usually CCed back to sender for traceability.
Autodiscover allows automatic quick and easy configuration of new client seamlessly without technical knowledge on all newer version of Outlook client on both PCs & Mac	Need some technical knowledge & server information in order to setup mail clients.
Share a mailbox among a group of users accessing the same views & interface.	Mailbox is not similiar without creating rules to cc copies of sent mails to sender. Contacts created are on each individual client’s address book. POP3 locks mailbox on access by each device & rendering mailbox inaccessible to others until mail download is complete. The process is further delayed with “leave-a-copy-on-server” option being set.
Mails, contacts & calendar entries are retained on both client & server. Failed client systems can resync & recover all mail items prior to failure.	If “leave a copy on the server” option is not set, mails are downloaded on client device and deleted from server. In event of disk failure on client system with no backups, all mails will be lost.
Native Exchange client support in Outlook.	No support or requiring connectors to work as Exchange client.
Mail retention policy enable retention of deleted email, to allow recovery or adhere to corporate policy or regulatory reasons.	No control on mail messages once they are downloaded.
Advanced messaging features like unified messaging system, instant messaging client, SSO (single sign on support), hybrid deployment, etc.	Not available or limited advanced features on other hosted services.
Can Support 2007, 2010. But, cannot support Office 2000, 2003	Can Support Outlook 2000, 2003, 2007, 2010, 2013

Office 365 Exchange Online – Executive Summary

Office 365 (Exchange Online) has a lot of good features that can really help the sophisticated office users to be more efficient and productive. One of the main strong feature is the ability to work across many devices anywhere and anytime over secured network.