As a cyber security company, we must have your organisational information protected from prying eyes.
While it may seem economical to use Webmail, after adding in financial risk into the picture, your resulting loss is much greater than just losing access.
Things like website downtime, will undoubtedly cause a loss of revenue, and if you don't have backups of your data, imagine how much time it would take to restore those from scratch. Even if you have employees that can type fast enough, that is still a negative balance in the bank.
These factors are not often included in the tabulation of using a Webmail service for email communications.
If you access your organisational data (like your financials, or client information), and use it with Webmail, this opens up a whole new opportunity for hackers, malware, and emerging cyber threats to attack your company, or bring down your architecture.
By keeping things separate, your company, be it a startup, SME, or enterprise; will have avoided a huge cyber security disaster. Let's not even start about cyber security insurance.