Domain names with Swedish characters such as Å, Ä and Ö are known as IDN domains (Internationalised Domain Names). Using them requires that the web browser and email program (mail client) both support IDN.
Browser and email support for IDN
Almost all modern web browsers support IDN domain names. Email support, however, is often more limited, so messages sent to or from an IDN-only address may not be delivered reliably.
Our recommendation
We usually recommend treating an IDN domain name as a complement to a transliterated domain name (a domain name without Swedish characters). Register both, point them to the same website, and use the transliterated version as your primary address for email.