small mail transfer agent listening on port 25 - useful on local server sometimes it crashs.. ^^

setup a correct (dns resolvable) hostname:

dpkg-reconfigure exim4-config

mailservers may block temporary dyndns IPs or move them to spam!

check for frozen messages:

mailq

remove all frozen messages from mailq:

exim -bp | exiqgrep -i | xargs exim -Mrm

not even a daemon. it just forwards mails. very simple and useful for websites and system to just send mail.

/etc/ssmtp/ssmtp.conf:

# The user that gets all the mails (UID < 1000, usually the admin)
root=username@gmail.com

# The mail server (where the mail is sent to), both port 465 or 587 should be acceptable
# See also https://support.google.com/mail/answer/78799
mailhub=smtp.gmail.com:587

# The address where the mail appears to come from for user authentication.
rewriteDomain=gmail.com

# The full hostname
hostname=localhost

# Use SSL/TLS before starting negotiation
UseTLS=Yes
UseSTARTTLS=Yes

# Username/Password
AuthUser=username
AuthPass=password

# Email 'From header's can override the default domain?
FromLineOverride=yes

info copied from: https://wiki.archlinux.org/index.php/SSMTP