OK, I'll test it later. Thanks.
However I can't resolve why Kmail works w/o problem. It is on the same PC, same ISP, same Mail Server, same accounts and same recipients for testing etc. The only difference is Kmail running on F7 on anoterh HD.
Edit - 1
The Mail Server is running serving several users. They already have their accounts created. Therefore I'll skip following steps
postconf -e 'home_mailbox = Maildir/'
postconf -e 'mailbox_command ='
useradd -d /home/sample_user -g users sample_user
$ ls /etc/postfix
dynamicmaps.cf master.cf sasl
main.cf postfix-files ssl
What are "virtual" and "virtual.db" for ???
$ sudo postconf -e 'virtual_maps = hash:/etc/postfix/virtusertable'
$ sudo postconf -e 'mydestination = /etc/postfix/local-host-names'
$ sudo nano /etc/postfix/local-host-names
copying following lines on it
example.com (Shall I retain this domain ???)
What is "example.com" for?? I don't have this domain on main.cf
$ sudo nano /etc/postfix/virtusertable
adding following lines on it
firstname.lastname@example.org user1 (OR user2 ???)
email@example.com user1 (OR user3 ???)
etc. (create above 3 lines for each user ???)
$ sudo postmap /etc/postfix/virtusertable
$ sudo /etc/init.d/postfix restart
Please advise to avoid making mistake and causing problem to existing users. TIA
Edit - 2:
I'm now on the same Workstation running F7. New discovery;
Evolution running on F7 works seamlessly. It can send and receive mails, with the same settings as on Ubuntu, via the Mail Server w/o problem. This discovery makes me considering that Evolution on Ubuntu may has no problem. Neither there is a problem on the Mail Server. Ubuntu may has some misconfiguration causing the problem on "Relay access denied".