You must log in with the full email address, not just the local part, so the username would be firstname.lastname@example.org
The server1.example.com point to 192.168.0.174. I did as instruction by putting 192.168.0.174 server1.example.com server1 in /etc/hosts file. I don't know what else needs to be done? I still can access only by IP address only.
Modify your client PC's host file and add a record for server1.example.com or set up a local DNS server that resolves server1.example.com.