OpenSMTPD
OpenSMTPD is a free mail transfer agent, developed as part of the OpenBSD project. This article builds upon Mail server.
Installation
Install the opensmtpd package.
Configuration
OpenSMTPD is configured in /etc/smtpd/.
Local mail
To have local mail working, for example for cron mails, it is enough to simply start smtpd.service.
The default configuration of OpenSMTPD is to do local retrieval and delivery of mail, and also relay outgoing mail. See smtpd.conf(5).
Local mail only
To do only local mail, the following is enough:
/etc/smtpd/smtpd.conf
listen on localhost action "local" mbox alias <aliases> match for local action "local"
Hybrid : local mail and relay
These two lines in /etc/smtpd/smtpd.conf :
action "local" mbox alias <aliases> action "relay" relay host "smtp://smtp.foo.bar" mail-from "@foo.bar" match for local action "local" match for any action "relay"
configure OpenSMTPD to :
- send local email locally, without going through a relay (useful for cron & at mail notifications)
- use a relay to send a mail outside of localhost
Simply replace smtp.foo.bar by your ISP mail server, or another server at your convenience.
Relay only
To send all local emails through a relay invoke procmail:
/etc/smtpd/smtpd.conf
action "local" mda "procmail -f -" virtual <aliases> action "relay" relay host "smtps://label@smtp.foo.bar" auth <secrets> mail-from "@foo.bar" match for local action "local" match for any action "relay"
The aliases option is used for the local user mapping, for a simplified mapping you can use virtual aliases with a catch all:
/etc/smtpd/aliases
@ foo@bar
Simple OpenSMTPD/mbox configuration
TLS
To obtain a certificate, see OpenSSL#Usage.
ciphers are not known to be insecure. You might still want to test the server as described in Server-side TLS.Create user accounts
- Create a user account on the mail server for each desired mailbox.
# useradd -m -s /bin/bash roger # useradd -m -s /bin/bash shirley
- OpenSMTPD will deliver messages to the user account's mbox file at
/var/spool/mail/<username> - Multiple SMTP email addresses can be routed to a given mbox if desired.
Craft a simple smtpd.conf setup
- A working configuration can be had in as little as nine lines!
/etc/smtpd/smtpd.conf
pki mx.domain.tld cert "/etc/smtpd/tls/smtpd.crt" pki mx.domain.tld key "/etc/smtpd/tls/smtpd.key" table creds "/etc/smtpd/creds" table vdoms "/etc/smtpd/vdoms" table vusers "/etc/smtpd/vusers" listen on eth0 tls pki mx.domain.tld listen on eth0 port 465 smtps pki mx.domain.tld auth <creds> listen on eth0 port 587 tls-require pki mx.domain.tld auth <creds> action receive mbox virtual <vusers> action send relay match from any for domain <vdoms> action receive match for any action send
Create tables
- For the domain table file; simply put one domain per line
/etc/smtpd/vdoms
personaldomain.org businessname.com
- For the user table file; list one inbound SMTP email address per line and then map it to an mbox user account name, SMTP email address, or any combination of the two on the right, separated by commas.
/etc/smtpd/vusers
roger@personaldomain.org roger newsletters@personaldomain.org roger,roger.rulz@gmail.com roger@businessname.com roger shirley@businessname.com shirley info@businessname.com roger,shirley contact@businessname.com info@businessname.com
- For the creds table file; put the user name in the 1st column and the password hash in the 2nd column
/etc/smtpd/creds
roger <password hash created using 'smtpctl encrypt' command> shirley <password hash created using 'smtpctl encrypt' command>
Test the configuration
# smtpd -n
If you get a message that says 'configuration OK' - you are ready to rock and roll. If not, work on any configuration errors and try again.
Troubleshooting
Console debugging
If you are having problems with mail delivery, try stopping the smtpd.service and launching the daemon manually with the 'do not daemonize' and 'verbose output' options. Then watch the console for errors.
# smtpd -dv
Subsystem tracing
Add the -T flag to get real-time subsystem tracing
# smtpd -dv -T smtp
Alternately, use the smtpctl trace <subsystem> command if the daemon is already running. The trace output will appear in the console output above as well as the journalctl output for the smtpd.service. For example:
# smtpctl trace expand && smtpctl trace lookup
...will trace both aliases/virtual/forward expansion and user/credentials lookups
Manual Submission port authentication
- Encode username and password in base64
# printf '\0username\0password' | base64
- Connect to submission port using
openssl s_clientcommand
# openssl s_client -host mx.domain.tld -port 587 -starttls smtp
- enter
ehlo myhostnamefollowed byAUTH PLAIN. Paste in the base64 string from step above after334response.
250 HELP ehlo test.domain.tld 250-mx.hostname.tld Hello test.domain.tld [5.5.5.5], pleased to meet you 250-8BITMIME 250-ENHANCEDSTATUSCODES 250-SIZE 36700160 250-DSN 250-AUTH PLAIN LOGIN 250 HELP AUTH PLAIN 334 dXNlcm5hbWUAdXNlcm5hbWUAcGFzc3dvcmQ= 235 2.0.0: Authentication succeeded
"Helo command rejected: need fully-qualified hostname"
When sending email, if you get this kind of messages, set your FQDN in the file /etc/smtpd/mailname. Otherwise, the server name is derived from the local hostname returned by gethostname(3p), either directly if it is a fully qualified domain name, or by retrieving the associated canonical name through getaddrinfo(3).
System users authentication failure
If you are using the system users and the authentication with valid credentials fails, you have to configure PAM:
/etc/pam.d/smtpd
auth required pam_unix.so account required pam_unix.so password required pam_unix.so session required pam_unix.so
See also
- Wikipedia:OpenSMTPD
- OpenSMTPD pairs well with Dovecot. Combine the two for a nice minimalist mailserver
- OpenSMTPD project page
- Simple SMTP server with OpenSMTPD