Also - have separate email stacks for communications and operations. Like it or not, your email is a low-friction way to get access to many of your other accounts, and maybe even a good way to LOSE access to some of your accounts. Your operational email domain should never be published, only used to register accounts and maybe do alerting, etc. You would whitelist senders. You would never use it to say anything, or associate with anyone, that someone might one day find offensive or controversial.
I have email addresses at .co.uk, .digital and .social never had deliverability issues with sending or receiving.
When I worked at a large (100m emails/wk) email service provider the key thing was sending IP reputation followed by things like DKIM and SPF DNS records on the sending domain.
IP reputation would be an issue if you self hosted your email, but using a reputable provider such as tutanota and fastmail should pose no issue.
We resolved it by pointing clients to use google dns.
Never had similar problems with .com
Do you mean you can lose your domain if your country leaves the EU, or are you talking about other issues?
.eu domains may only be registered to a person or entity that exists within the EU. As soon as Brexit crystallised any British person or entity owning a .eu domain was unable to renew it unless they had an address they legally occupied within an EU country.
I know a few companies who rented a small amount of office space in France so that they could retain their .eu domain.
Their email service is likely to have some credibility from the global anti-spam force. They probably have the budget for best practices and reasonable security. As you mention .de domains: The online legal text generators for Impressum/Datenschutzerklärung are likely to have the correct text fragments to use for larger vendors. Overall they just have to uphold some level of reputation I hope.
Example: ionos.de
