Thunderbird community manager here. This is correct. Moving from the Mozilla Foundation (non-profit) meant we had to cancel recurring donations.

We hope everyone will resume via https://give.thunderbird.net

There's no continuing option to give to the Foundation and direct support to Thunderbird? Since the new subsidiary is for-profit, direct donations will no longer be tax-deductible.

Feels like an odd choice (and perhaps, an important omission?) when the announcement calls out the importance of donations to Thunderbird.

I doubt it's legal for money to flow that way?

You'd be donating to a nonprofit and getting the tax benefit, then the nonprofit would be passing it onto a for-profit corporation. End result: tax-deductible donation to a for-profit corp. That doesn't sound like something the IRS would like.

It sounds like the ability to directly generate revenue was seen as outweighing the benefit of allowing tax-deductible donations. (This is my own speculation.)

Consider it this way: if a non-profit pays a for-profit company for services rendered (pure expense on the balance sheet), are they "passing on" your donation to the for-profit? I would think not. Non-profits need to be able to pay for things. At the most basic office-management level, they would need to rent office space, buy paper and coffee filters, contract a janitorial service, etc.

Would there be a limit? I don't think so. If I was running, say, a non-profit website host, 100% of my raised donations would be going, as expenses, to a for-profit company (some commercial cloud-hosting provider.) That's still an entirely-legitimate model for a non-profit to operate under.