msmtp is a Social & Communication software developed by Martin Lambers. After our trial and test, the software is proved to be official, secure and free. Here is the official description for msmtp:
Brothersoft Editor: 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.
Sendmail compatible interface (command line options and exit codes). Authentication methods PLAIN, LOGIN, CRAM-MD5, DIGEST-MD5, GSSAPI, and NTLM. 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. Fast SMTP implementation using command pipelining. Support for Internationalized Domain Names (IDN). DSN (Delivery Status Notification) support. RMQS (Remote Message Queue Starting) support (ETRN keyword). IPv6 support. Support for multiple accounts. you can free download msmtp 1.4.24 now.