I'm following the mailman guide but couldn't locate /etc/postfix/ so created it as follows:

root@dur:~# 
root@dur:~# cat /etc/postfix/transport
dur.bounceme.net      mailman:
root@dur:~# 
root@dur:~# telnet localhost 25
Trying 127.0.0.1...
Connected to localhost.
Escape character is '^]'.
220 dur.bounceme.net ESMTP Postfix (Ubuntu)
ehlo fqdn_test
250-dur.bounceme.net
250-PIPELINING
250-SIZE 10240000
250-VRFY
250-ETRN
250-STARTTLS
250-ENHANCEDSTATUSCODES
250-8BITMIME
250 DSN
mail from:[email protected]
250 2.1.0 Ok
rcpt to:thufir@localhost
451 4.3.0 <thufir@localhost>: Temporary lookup failure
rcpt to:[email protected]
451 4.3.0 <[email protected]>: Temporary lookup failure
quit
221 2.0.0 Bye
Connection closed by foreign host.
root@dur:~# 
root@dur:~# postconf -n
alias_database = hash:/etc/aliases
alias_maps = hash:/etc/aliases, hash:/var/lib/mailman/data/aliases
append_dot_mydomain = no
biff = no
broken_sasl_auth_clients = yes
config_directory = /etc/postfix
default_transport = smtp
home_mailbox = Maildir/
inet_interfaces = loopback-only
mailbox_command = /usr/lib/dovecot/deliver -c /etc/dovecot/conf.d/01-mail-stack-delivery.conf -m "${EXTENSION}"
mailbox_size_limit = 0
mailman_destination_recipient_limit = 1
mydestination = dur, dur.bounceme.net, localhost.bounceme.net, localhost
myhostname = dur.bounceme.net
mynetworks = 127.0.0.0/8 [::ffff:127.0.0.0]/104 [::1]/128
readme_directory = no
recipient_delimiter = +
relay_domains = lists.dur.bounceme.net
relay_transport = relay
relayhost =
smtp_tls_session_cache_database = btree:${data_directory}/smtp_scache
smtp_use_tls = yes
smtpd_banner = $myhostname ESMTP $mail_name (Ubuntu)
smtpd_recipient_restrictions = reject_unknown_sender_domain, reject_unknown_recipient_domain, reject_unauth_pipelining, permit_mynetworks, permit_sasl_authenticated, reject_unauth_destination
smtpd_sasl_auth_enable = yes
smtpd_sasl_authenticated_header = yes
smtpd_sasl_local_domain = $myhostname
smtpd_sasl_path = private/dovecot-auth
smtpd_sasl_security_options = noanonymous
smtpd_sasl_type = dovecot
smtpd_tls_auth_only = yes
smtpd_tls_cert_file = /etc/ssl/certs/ssl-mail.pem
smtpd_tls_key_file = /etc/ssl/private/ssl-mail.key
smtpd_tls_mandatory_ciphers = medium
smtpd_tls_mandatory_protocols = SSLv3, TLSv1
smtpd_tls_received_header = yes
smtpd_tls_session_cache_database = btree:${data_directory}/smtpd_scache
smtpd_use_tls = yes
tls_random_source = dev:/dev/urandom
transport_maps = hash:/etc/postfix/transport
root@dur:~# 
root@dur:~# tail /var/log/mail.log
Aug 28 02:05:15 dur postfix/smtpd[20326]: connect from localhost[127.0.0.1]
Aug 28 02:06:10 dur postfix/smtpd[20326]: warning: hash:/var/lib/mailman/data/aliases is unavailable. open database /var/lib/mailman/data/aliases.db: No such file or directory
Aug 28 02:06:10 dur postfix/smtpd[20326]: warning: hash:/var/lib/mailman/data/aliases lookup error for "thufir@localhost"
Aug 28 02:06:10 dur postfix/smtpd[20326]: NOQUEUE: reject: RCPT from localhost[127.0.0.1]: 451 4.3.0 <thufir@localhost>: Temporary lookup failure; from=<[email protected]> to=<thufir@localhost> proto=ESMTP helo=<fqdn_test>
Aug 28 02:06:23 dur postfix/smtpd[20326]: warning: hash:/var/lib/mailman/data/aliases is unavailable. open database /var/lib/mailman/data/aliases.db: No such file or directory
Aug 28 02:06:23 dur postfix/smtpd[20326]: warning: hash:/var/lib/mailman/data/aliases lookup error for "[email protected]"
Aug 28 02:06:23 dur postfix/smtpd[20326]: NOQUEUE: reject: RCPT from localhost[127.0.0.1]: 451 4.3.0 <[email protected]>: Temporary lookup failure; from=<[email protected]> to=<[email protected]> proto=ESMTP helo=<fqdn_test>
Aug 28 02:06:28 dur postfix/smtpd[20326]: disconnect from localhost[127.0.0.1]
Aug 28 02:06:49 dur dovecot: pop3-login: Login: user=<thufir>, method=PLAIN, rip=127.0.0.1, lip=127.0.0.1, mpid=20338, TLS
Aug 28 02:06:49 dur dovecot: pop3(thufir): Disconnected: Logged out top=0/0, retr=0/0, del=0/0, size=0
root@dur:~# 

The manual page is here.