configure Ubuntu to send mail (as an SMTP client using postfix)

  1. We will start with a trusty DigitalOcean instructional – at least step 1 of that instructional.
  2. I want to send mail using mailgun, which allows for ports 25, 587 and 465 (SSL/TLS). I’ll use 587 which is called submission in postfix terminology, I guess due to 587 being the proper port for TLS email submission. Because I want to use encryption (SASL) (or whatever), I need to setup Postfix accordingly. I changed my Postfix config file as such
     ubuntu@machine_name:~$ sudo nano /etc/postfix/main.cf
    #various stuff above
    relayhost = [smtp.mailgun.org]:submission
    mynetworks = 127.0.0.0/8 [::ffff:127.0.0.0]/104 [::1]/128
    mailbox_size_limit = 20000000
    recipient_delimiter = +
    inet_interfaces = all
    inet_protocols = all
    smtp_sasl_auth_enable = yes
    smtp_tls_security_level = encrypt
    smtp_sasl_security_options=noanonymous
    smtp_sasl_password_maps = hash:/etc/postfix/sasl_passwd

    Some of these settings are related to the DigitalOcean instructional, such as custom mailbox_size_limit. Make sure all the smtp settings are there

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