I can't speak for Foundation, but I do know that - especially with outgoing emails - self-hosting these days is a pretty big challenge.
Some providers will immediately flag your emails or delete them outright due to too strict firewall settings. Imagine a customer not receiving a response because their email provider didn't let Foundation team's reply through. That will probably be the main issue.
Sure it can happen, but every serious company in the world have their own email with domains, it would be silly if everyone would use just gmail.
Blocking usually happens if people are using shared hosting, and I am not 100% sure but I think that ledger and trezor considered switching to self-hosted emails after leaking of their newsletter with third party partners.
Oh, it's not about using a Gmail domain; Foundation Devices do have their own domain and use it for support emails. It just appears on the backend they use Google.
And that's what the vast majority of companies does (if it's not Google, it's a different third party email provider), no matter what the domain is, which you see as an end customer.
As far as I know, truly self-hosting your IMAP and SMTP and getting all emails to come through is one of the hardest things on the internet..
But I'd be happy to be proven wrong e.g. through a written guide on how to set up self-hosted email with high success rate!
Edit: I've looked around a bit, and it seems possible, but fiddly. It's possible to land on a blacklist and then need to get un-blacklisted manually.Self-hosting email in 2020 – Joe Nobody vs. World [02/2020]
Outlook.com is blocking my mail server [07/2020]
Outlook.com is no longer blocking my mail server [08/2020]
Now, this is a private person hosting their own private email account. If something like that happens, it's probably not critical.
But imagine what happens if as a company, you appear going 'MIA' in a support discussion or appear to be completely unresponsive to support requests, because their replies land in your spam folder.
Even one day of this can cause significant harm to a company's reputation.
Now, neither do I want to be the 'weird nerd' jumping in to protect a certain company, nor do I know for sure that this is the reason why Foundation Devices doesn't host their own support emails.
I just wanted to inform everyone who believes this to be a trivial task that it's really not.
Personally, I'd prefer not to get Foundation Devices emails for a day or two (because of landing on my email provider's blacklist or whatever)), but I kind of understand the rationale.
I also do believe it would be possible for Foundation to move to a self-hosted server, and prior to that inform customers about the change and that they might need to check their spam folder or explicitly whitelist them.
It would also be possible to write a blog post about it and link it just below the support form, so that new customers know why they may not be receiving a reply.