POP3 connect error.

Exchange 2019 standalone new installation. POP3 allowed, POP3-service running, mailbox created. Mailbox is accessible by OWA. When I try to connect manually to the POP3 server I got an error:
+OK The Microsoft Exchange POP3 service is ready.
USER 1CUser
+OK
PASS MYPassWord826
-ERR Server Unavailable. 21