Dovecot is necessary to make the mail available from the outside of the server. It's an imap and pop3 server.
It is pretty hard to configure, and the doc in it's wiki is hard to find. But once the doc find, you have all the debugging tools available.
The main configuration is in /etc/dovecot/dovecot.conf and, of course, dovecot have to be initiated in the services run levels and is after that available as rcdovecot or better systemctlm start dovecot.service.
The base directory is /var/run/dovecot
I just changed the config file
(add at the end of the file):
protocols = imap pop3 disable_plaintext_auth = no mail_location = mbox:~/mail:INBOX=/var/mail/%u
/etc/dovecot/conf.d/20-imap.conf imap_max_line_length = 128k mail_max_userip_connections = 20
For imap (the only choice I used), you need to open the port 143 (imap) on the firewall. 110 for pop3.
After installing on openSUSE, the user dovecot:dovecot already exists. System is not crypted.
On the client side, configure Thunderbird for your new server and test to see if it receive mails. It should :-).
Doveconf is an utility that allows to know what parameter is active
# doveconf protocols listen
for example may give as result:
protocols = imap pop3 listen = *, ::
See the dovecot page.
Notice we exit a telnet session with ". logout" (dot, espace, logout).
I used mail_location = mbox:~/mail:INBOX=/var/mail/%u as mail location. With this config for an imap server, the INBOX is shared in /var/spool/mail (/var/mail is a link to /var/spool/mail) where it can be seen by other mail systems (like mailx), but the other imap folders are in the users home. Experienced users usually do not keep mails in INBOX, but filter them to various folders, but many unexperienced users do store all in INBOX. So you have to keep an eye to both / (where is /var located in my system) and in /home.
Usually, mailboxes are sort of MB, not GB, but in a near future, when most people will have fiber connections, sending Gb by mail could become currrent.
Dovecot is installed through YaST, so should be updated automatically.