msmtp is an open source 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.

Supported SMTP features include:
1. Authentication methods PLAIN, LOGIN, CRAM-MD5 and EXTERNAL (and GSSAPI, DIGEST-MD5 and NTLM when compiled with GNU SASL support)
2. TLS encrypted connections with the OpenSSL or GnuTLS libraries (including server certificate verification and the possibility to send a client certificate)
3. Support for Internationalized Domain Names (IDN)
4. DSN (Delivery Status Notification) support
5. PIPELINING support for increased transmission speed
6. RMQS (Remote Message Queue Starting) support (ETRN keyword)

In addition to sendmail mode, there are two other modes of operation:
1. Server information mode. In this mode, msmtp prints as much information as it can get about a given SMTP server (supported features, maximum mail size, ...).
2. Remote Message Queue Starting mode. In this mode, msmtp sends a Remote Message Queue Starting request for a host, domain, or queue to a given SMTP server.

Normally, a system wide configuration file and/or a user configuration file contain information about which SMTP server to use and how to use it, but almost all settings can also be configured on the command line.

Optional features, depending on external libraries (see the file INSTALL for usage instructions):
TLS/SSL support
You need either GnuTLS >= 1.2.0 or OpenSSL >= 0.9.6 for TLS/SSL support. It is also possible to disable TLS/SSL support entirely.

Additional authentication methods
The built-in authentication code supports the PLAIN, LOGIN, CRAM-MD5, and EXTERNAL mechanisms. When GNU SASL support is enabled, some or all of the mechanisms EXTERNAL, GSSAPI, DIGEST-MD5, CRAM-MD5, PLAIN, LOGIN, and NTLM are available, depending on the compile-time options used for libgsasl. GNU SASL >= 0.2.4 is required.

Native language support (NLS)
On systems other than GNU/Linux, you need GNU gettext if you want NLS.

msmtp Features:
1. Sendmail compatible interface (command line options and exit codes).
2. Authentication methods PLAIN, LOGIN, CRAM-MD5, DIGEST-MD5, GSSAPI, and NTLM.
3. TLS/SSL both in SMTP-over-SSL mode and in STARTTLS mode. Full certificate trust checks can be performed. A client certificate can be sent.
4. Fast SMTP implementation using command pipelining.
5. Support for Internationalized Domain Names (IDN).
6. DSN (Delivery Status Notification) support.
7. RMQS (Remote Message Queue Starting) support (ETRN keyword).
8. IPv6 support.
9. Support for multiple accounts.

The license of this software is Free, you can free download and free use this email tool software.