install postfix dovecot ubuntu 16.04

Shell
smtpd_banner = $myhostname ESMTP $mail_name
biff = no

# appending .domain is the MUA's job.
append_dot_mydomain = no
readme_directory = no

#SMTP CONFIGURATION
smtp_use_tls=yes
smtp_tls_security_level = may
smtp_tls_session_cache_database = btree:${data_directory}/smtp_scache

# SMTPD CONFIGURATIONS
# SMTPD AUTHENTICATION

smtpd_sasl_auth_enable = yes
smtpd_sasl_type = dovecot
smtpd_sasl_path = private/auth


# SMPTD TLS

smtpd_use_tls=yes
smtpd_tls_security_level = may
smtpd_tls_session_cache_database = btree:${data_directory}/smtpd_scache

smtpd_tls_cert_file=/etc/letsencrypt/live/example.com/fullchain.pem
smtpd_tls_key_file=/etc/letsencrypt/live/example.com/privkey.pem

myhostname = mail.example.com
myorigin = /etc/mailname
mydestination =  localhost.$mydomain, localhost
relayhost = 
mynetworks = 127.0.0.0/8 [::ffff:127.0.0.0]/104 [::1]/128
mailbox_size_limit = 0
recipient_delimiter = +
inet_interfaces = all
inet_protocols = all
alias_maps = hash:/etc/aliases
alias_database = hash:/etc/aliases
virtual_transport = lmtp:unix:private/dovecot-lmtp
virtual_mailbox_domains = /etc/postfix/virtual_mailbox_domains
Source