edit: As mentioned by a sibling comment, my email is currently on Fastmail, zero problems.
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.
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
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.
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
Care to explain which are those concerns about privacy that you may find when owning a custom email address? Thanks in advance.
https://fastmail.blog/advanced/why-we-dont-offer-pgp/
I don't believe the encryption/key management from a company.
protonmail is great as a secure disposable email, but as a go-to daily email service I found it too difficult to manage. Hard to use other email clients due to requiring this bridge, and their mobile apps and web guis are just not up-to-par with other offerings. Being able to use any frontend on mobile (and not deal with complicated proxy setups) was my biggest issue.
Using a custom domain has made the switches easier, as I don't have to tell anyone to update their contacts or worry about forwarding. Just exporting/importing, change some MX records, and I can switch providers any time.
Swapping from Protonmail to Fastmail was super easy. Exported all my email, imported into Fastmail, and swapped over the DNS records. Took me a couple of hours in between other tasks.
Besides, FastMail exists before Gmail and the people in FastMail are active standard protocol developers like IMAP and recently JMAP (a modern mail protocol will replace SMTP/IMAP, FastMail as a reference implementation), which is good because at least I know they understand the protocol and implement it by themselves.
It’s really fast, but come on, that’s one low bar to jump over. Gmail is the electron of mail interfaces.
Originally my reason to choose them instead of Protonmail was that Protonmail only works with their official client, which is a far too limiting dependency in my eyes.
I'm quite positive on it, nice interface and unique useful features, and it's reliable in my experience. However you have to be ok with its particularities, mainly that it doesn't have IMAP, and it's expensive.
Ultimately it's for people who love their unique interface/features, and don't mind paying so much for email.