Lightweight outgoing SMTP server

Question

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.

Answer 1

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.

Answer 2

There are several choices of minimal, relay-only mail transfer agents (MTAs, or "mail servers"), some of which have been mentioned in other answers:

• esmtp http://esmtp.sourceforge.net/
• nullmailer http://untroubled.org/nullmailer/ (my personal favourite)
• sSMTP http://packages.debian.org/source/sid/ssmtp (development has stopped, i think)

For either of those to work, you need a full fledged MTA somewhere that will further relay your messages (known as "mail hub").

Answer 3

ESMTP is a relay only mail transfer server that may work for your application.

Answer 4

IMHO, the easiest way to do this is to install postfix (if debconf asks you questions, pick "internet site"), then run these commands:

postconf -e relayhost=other.mailserver.com
postconf -e mailname=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 mailname parameter will be the default domain name. So if you send mail to foo it will go to foo@my.domainname.com. Mail sent by user bar will be from bar@my.domainname.com.

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.

Answer 5

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. Just stay the hell away from sendmail. :-)

Answer 6

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="me@example.com jab@example.com" echo "Test Content" | mail -s "Test Subject" $listoftargets

On some systems, there is already a minimal mailserver for sending only.

Sam T.

Answer 7

If you have no particular affinity for one system over another, there is a software designed just for this: ssmtp. The ssmtp configuration file, using a GMail example:

Root=your_email@gmail.com
Mailhub=smtp.gmail.com:465
RewriteDomain=gmail.com
AuthUser=me@gmail.com
AuthPass=your_gmail_password
FromLineOverride=Yes
UseTLS=Yes

Your system will then send mail through Gmail, using localhost as outgoing SMTP server in your applications. It is a tiny program, and it is not a daemon.