SMTP clients

This page lists SMTP and SMTPS clients available on OpenWRT, that are able to send email to other email servers.

The table shows all clients ported to OpenWrt:

Name Version Dependencies Size Features
BusyBox sendmail 1.33 must be compiled libopenssl 14KB SSL, smarthost only, sendmail-compatible, SMTP auth
msmtp 1.8 libgnutls 51KB SSL, smarthost only, sendmail-compatible, SMTP auth
msmtp-nossl 1.8 47KB smarthost only, sendmail-compatible, SMTP auth
mailsend 1.19 libopenssl 39KB SSL, smarthost only, no configuration required, MIME, attachements, IPv6, SMTP auth
mailsend-nossl 1.19 37KB smarthost only, no configuration required, MIME, attachements, IPv6, SMTP auth
ssmtp 2.64 libopenssl 11KB SSL support, smarthost only, SMTP auth. No longer available since OpenWRT 21
mini-sendmail no package 5KB smarthost only, no configuration required. No longer available since OpenWRT 17
emailrelay 2.3 libc libssp libopenssl libstdcpp 350KB SMTP proxy and store-and-forward message transfer agent (MTA); can be used similar to postfix with mail queue in combination with msmtp and mutt. In v2.5 can deliver mail directly. See emailrelay
XMail no package libopenssl

“smarthost only” means that the program is only capable to send email through a configured “smarthost”, that is, it cannot directly deliver to the destination SMTP server. E.g. it won't make a DNS lookup of the email address for MX record.

Mailsend is a simple command line program to send mail via SMTP protocol.

Being quite lightweight and not requiring any configuration, mailsend is ideal for sending mails in shell scripts. - Sources and issues

Depending on whether you want SSL support or not (actually, the size of libopenssl will probably be the decisive factor), install one of the two versions:

opkg install mailsend
opkg install mailsend-nossl

Simple usage:

mailsend -f root@openwrt -t -smtp -sub "My subject" -msg-body /tmp/body

For advanced usage (MIME attachements, authentication, BCC, etc), see:

mailsend -h
mailsend -example
msmtp is an SMTP client. In the default mode, it transmits a mail to
an SMTP server (for example at a free mail provider) which does the
delivery. To use this program with your mail user agent (MUA), create
a configuration file with your mail account(s) and tell your MUA to
call msmtp instead of /usr/sbin/sendmail.

Since msmtp understands standard sendmail options, it can be used in places where sendmail is expected (e.g. PHP code).

Official site - Sources and documentation

opkg install msmtp

Place your configuration in /etc/msmtprc. There is an existing default-block in the included config file so if you want to call msmtp without specifying an account, then you need to rename the existing default-block to something else.

Here is an example configuration using Gmail that worlks with 2FA and an app password:

# Example for a system wide configuration file

# A system wide configuration file is optional.
# If it exists, it usually defines a default account.
# This allows msmtp to be used like /usr/sbin/sendmail.
# cat /etc/msmtprc

account default

port 465
auth on
tls on
tls_starttls off

password app_passwd_here

syslog LOG_MAIL

Now symlink msmtp to sendmail with ln -s /usr/bin/msmtp /usr/sbin/sendmail.

Also you may configure env variables EMAIL for From address and SMTPSERVER to specify smarthost.

echo -e "Subject: Test mail\n\nThis is a test \"message\"." | sendmail -f "<something@your-domain.tld>" "<recipient@destination.tld>"

Note that sendmail (/usr/sbin/sendmail) is a symlink to /usr/bin/msmtp.

Name Version Dependencies Size Description
mini-sendmail 1.3.6-4 none 5866 mini_sendmail reads its standard input up to an end-of-file and sends a copy of the message found there to all of the addresses listed. The message is sent by connecting to a local SMTP server. This means mini_sendmail can be used to send email from inside a chroot(2) area.

Official site

opkg install mini-sendmail

On Chaos Calmer, the package is no longer available, but the version from Barrier Breaker still works (AA & BB versions as installed below work in AA):

opkg install
mini_sendmail -p465 -t < input_file
usage: mini_sendmail [-f<name>] [-t] [-s<server>] [-p<port>] [-T<timeout>] [-v] [address ...]

Note that there must not be a space between the option and the value; e.g. “-p 465” is incorrect.

Several sample configurations found on the internet failed, but as of 160413, this worked

echo -e 'From:\r\nSubject: Test Subject\r\n\r\nTesting\r\n.' | mini_sendmail failed; omitting -f failed; omitting “From: ” resulted in transmission, but no sender shown.

This is a very small package if you can find an smtp server which works and you can configure the command so that the server accepts it.

A secure, effective and simple way of getting mail off a system to your
mail hub. It contains no suid-binaries or other dangerous things - no
mail spool to poke around in, and no daemons running in the background.
mail is simply forwarded to the configured mailhost. Extremely easy
opkg install ssmtp

ssmtp expects its two configuration files named /etc/ssmtp/revaliases and /etc/ssmtp/ssmtp.conf. Both are self-explaining:

# /etc/ssmtp/ssmtp.conf
# /etc/ssmtp/revaliases
# Format: local_account:outgoing_address:mailhub

To use the program, with SMTP auth:

<code bash>
cat /etc/banner | ssmtp -vvv -auultranerd@universum.tb -ap123password456

The BusyBox sendmail is a smallest possible implementation but it must be compiled. It works only in smarthost mode.

Enable the applet during compilation in menuconfig: BusyBox options, Mail and sendmail. Additionally you may want to enable makemime applet that helps to send files with attachments.

You need to configure SMTPHOST env variable with the smarthost SMTP server to use. Instead of the variable you may use an option -S server[:port] to specify the SMTP server.

You may also need SMTP_ANTISPAM_DELAY env to bypass the Greylisting antispam if it enabled for submission.

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  • Last modified: 2023/04/02 10:56
  • by stokito