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What do you use as a lightweight SMTP for outgoing e-mails only?
I am running an app that sends e-mails via SMTP when events occur once in a while, and I don't need a fully featured e-mail server.
EDIT: I am more than happy to use something like postfix (and do), if that's the best choice. I was thinking there may be something much simpler, that runs out the box.
There are several choices of minimal, relay-only mail transfer agents (MTAs, or "mail servers"), some of which have been mentioned in other answers:
For either of those to work, you need a full fledged MTA somewhere that will further relay your messages (known as "mail hub") and it is strongly recommended that you control this mail hub. Bad Things™ can happen otherwise.
IMHO, the easiest way to do this is with postfix. You can configure it as a light outgoing relay with these commands:
postconf -e relayhost=other.mailserver.com
postconf -e myorigin=my.domainname.com
As long as the SMTP server specified in relayhost doesn't require authentication, allows you to relay or is a valid destination for the recipient address this will work.
The myorigin parameter will be the default domain name. So if you send mail to foo it will go to [email protected]. Mail sent by user bar will be from [email protected].
If you do need to authenticate and want to support TLS, also run the following commands:
postconf -e smtp_tls_security_level=may
postconf -e smtp_sasl_auth_enable=yes
postconf -e smtp_sasl_password_maps=pcre:/etc/postfix/sasl_password_maps
Then in /etc/postfix/sasl_password_maps have this content:
/./ username:password
All mail will be sent to your relayhost with the specified username and password.
relayhost=other.mailserver.com:465 then smtp_tls_wrappermode=yes and smtp_tls_security_level=encrypt but it's attempting to use the local user as the auth. I have to rewrite the auth user somehow.
Jun 29, 2016 at 4:13
Assuming you need a program you can run from the shell like sendmail(8), perhaps MSMTP will fit your needs? It can connect to a remote SMTP server and submit mail it gets as stdin, just like sendmail.
You may find sSMTP suitable for your needs. Read this article on it and its limitations.
Honestly though, I wouldn't be too stressed about installing postfix or exim, even if it is only for sending emails.
If you use docker, https://hub.docker.com/r/zixia/simple-mail-forwarder/ is a good choice for easy deploy and only of 10MB size, with full smtp(tls) support.
You technically don't need an e-mail server on your host, what you need (and probably already have) is an smtp-client (or MUA) that can connect to your corporate SMTP Server (which could be anywhere you can connect to.)
Depending on the App (and the programming language it was written in) there are many different ways for your app to connect to the 'the' SMTP Server on your network.
Usually, with PHP or Python, there's a configuration file with the app to specify the "SMTP" Server (which can be on your host or elsewhere on your network.) If you already have a mail server on the network, then just point the configuration to that server.
If no other options exist, the app can generate the e-mail message to standard output that you can process with something like:
listoftargets="[email protected] [email protected]" echo "Test Content" | mail -s "Test Subject" $listoftargets
On some systems, there is already a minimal mailserver for sending only.
Sam T.
mail or sendmail named executables. System notifications. That's the whole point isn't it? For anything else there are no constraints.
Jul 14, 2018 at 22:20
apt install postfix (will also restart config if installed)
Edit this config file: vi /etc/postfix/main.cf
Uncomment this line or use this sed:
sed -i 's/#smtp_sasl_security_options/smtp_sasl_security_options/' /etc/postfix/main.cf
Add your smtp info and reload service:
echo '[smtp.gmail.com]:587 <your_email>:<your_password>' > /etc/postfix/sasl_passwd && chmod 600 /etc/postfix/sasl_passwd (or [smtp.sendgrid.net]:587 apikey:xxx)
postmap /etc/postfix/sasl_passwd && systemctl reload postfix
Test it:
EMAIL=<your_email_address>
mail $EMAIL <<< "message" works.. or also(sendmail -f $EMAIL $EMAIL <<< "message")
Weekly postive control test message:
echo "mail -s "email test on: $(hostname)" root \<\<\< "email_test" > /etc/cron.weekly/email_test or if using .env/file:
echo "mail -s "email test on: $(hostname)" \$(cat ~/.env/EMAIL)" \<\<\< "email_test" > /etc/cron.weekly/email_test
To use one email forwarding for all root mail:
echo "your_email_address" >> /etc/aliases && newaliases and test with:
echo "body" | mail -s "subject" root
Now all apps mailing to root will go to your email. More info here:
https://www.digitalocean.com/community/tutorials/how-to-install-and-configure-postfix-as-a-send-only-smtp-server-on-ubuntu-16-04#step-3-testing-the-smtp-server
