Postfix

Preferir resolución LOCAL antes que DNS

lmtp_host_lookup = native
smtp_host_lookup=native
#disable_dns_lookups = yes
ignore_mx_lookup_error = yes

Errores comunes

Error :

postfix/postdrop[13652]: warning: unable to look up public/pickup: No such file or directory

Solución

sudo mkfifo /var/spool/postfix/public/pickup
sudo /etc/init.d/postfix restart