I suspect corporate is hooked on exchange, not outlook. Outlook 365 just goes along for the ride.
The jump from "providing an email client" to "providing a privacy focus email service for independent professionals and small businesses" is already quite large. Being able to sell that by giving some guarantees (in signed SLA form) is yet another jump on an entirely different scale.
Then look no further than public institutions, where (leaving everything else aside) almost every tender is public [0]. You'll never see Thunderbird in any of the submitted bids because there's no company behind it to write the bid and put its weight behind it.
It's a good canary to see if a service or product has anyone capable of supporting it, or if it can be monetized in any way. This doesn't have to be the developer, just any company that can realistically push it into the corporate world.
For smaller companies, or companies that want to invest less in their technology stack IT department, it sounds like a better deal to have all services provided and backed by a larger computation corporation (even if that's not always actually cheaper in the long run).
You can go quite a ways with that before you would get close to breaking even on even a single dedicated IT person. Assuming their cloud services etc. fit your business needs of course - but that's an awful lot of companies.
I agree that this is a sticking issue; most procurement offices have vendor/supplier questionnaires that ask about their cash flows etc., because companies want to deal with going concerns. FOSS without an org doesn't check that box.
BUT isn't this exactly the point of having a Mozilla Corporation, as separate from the nonprofit???
That's just the "smaller" half the story.
> isn't this exactly the point of having a Mozilla Corporation
This is the critical part. If I am using Thunderbird (or the hypothetical mail service discussed above) in my company today and have an issue or request (bug, configuration error, need assistance with a deployment, want additional features in the product, want additional integration with other products) can I contact someone directly and know that this will be treated according to my specific expectations?
In other words can I call someone at Mozilla Corporation now and ask for dedicated tech support, for a bug fix in a specified time frame, for a consultant to listen to my needs and come up with a solution? Because if my business relies on that product or service and I get no guarantees then I won't be happy to pay you just so I can queue up on Github and raise issues, and I'll go with %prominent software vendor% who gives me that.
RedHat doesn't sell you "Linux", they sell everything that comes with it, and create an entire ecosystem to go with that (partners that offer certification, training, consultancy and support, dev support, etc.).