Ubuntu – How is Ubuntu able to send alerts to external e-mail addresses

I finally found a detailed set of instructions by Tony Scelfo that actually work. It appears that you have to use transport layer security (TLS) on port 587. I have not gotten SSL SMTP to work.

First run sudo dpkg-reconfigure exim4-config and use these config options:

• General type of mail configuration: mail sent by smarthost; received via SMTP or fetchmail
• System mail name: <your hostname>
• IP-address to listen on for incoming SMTP connections: 127.0.0.1
• Other destinations for which mail is accepted: <your hostname>
• Machines to relay mail for: <leave this blank>
• IP address or host name of the outgoing smarthost: mail.example.com::587
• Hide local mail name in outgoing mail?
  • Yes - all outgoing mail will appear to come from your gmail account
  • No - mail sent with a valid sender name header will keep the sender’s name
• Keep number of DNS-queries minimal (Dial-on-Demand)? No
• Delivery method for local mail: <choose the one you prefer>
• Split configuration file into small files? Yes (you need to edit one of the files next)

Then run sudo vi /etc/exim4/passwd.client and add the following lines for your mail host, and any aliases it has (found through nslookup). Substitute <email address> and <password> with the account you want to route mail through):

mail.example.com:<email address>:<password>
mail.yourhosting.provider:<email address>:<password>

Once you edit the passwd.client file, run sudo update-exim4.conf which will integrate your changes into your Exim4 config.

Run sudo /etc/init.d/exim4 restart and make sure that the service stops and starts properly. If the service is unable to restart, something probably went wrong when you edited the passwd.client file.

If Exim4 restarted, go ahead and run sudo tail -f /var/log/exim4/mainlog to watch the mail logs. In a different window, send an email from your system and make sure that you see a record go by withR=smarthost T=remote_smtp_smarthost H=gmail-smtp-msa.l.google.com ... X=TLS-1.0:RSA_ARCFOUR_MD5:16 in it. The X=TLS means that the mail is being sent with transport layer security which is what you want.

From [1] pg 832

Another parameter we should set is mydestination, which specifies the mail domains that are local.

The changes which are relevant to my question:

Change the mydestination setting in /etc/postfix/main.cf to be blank.

mydestination = 

run

sudo postfix reload

[1] Unix and Linux system administration handbook, 4ed, 0-13-148005-7, 978-0-13-148005-6