Given how wrong the rest of the comment was, confusing mail client and mail server seemed like small potatoes. Especially when it can be argued that mail flows through the client if you squint a bit.

What was wrong with the rest of the comment?

Many enterprises have moved to Microsoft 365. Which uses Outlook.com and not Exchange.

The mail service in Microsoft 365 is called Exchange Online and it‘s based on Microsoft Exchange. Outlook.com (formerly) seems to have been been moved to the same infrastructure as Microsoft 365.

It's hosted (at Microsoft), but it's still Exchange. Though maybe there's a lower-end, non-Exchange option?

In any case, the article is a little confused.