Most apps only need your address and password. They ask us for the rest.
On iPhone, iPad or Mac? One switch to watch.
The ports Apple Mail fills in are correct. The one thing that still bites is Automatically manage connection settings, which arrives switched on and can move you to a port that refuses to send.
Other, Add Mail Account.IMAP. Host name mail.nyxe.app on both servers.It sent without signing in. Put your address and password on the outgoing server.
Use your whole address as the user name, on both servers.
Your address and your password are the whole of it.
IMAP 993 · SMTP 465 or 587 · TLS on every port