Kyle Pericak
"It works in my environment"
Postfix Send-Only Mail Service
Category:systems administrationTags:emailpostfix;
In order to send emails from a VM you need a mail server. Often you can use a public, corproate, or cloud mail server, but sometimes you might need to deploy your own locally.
This guide covers how to configure Postfix as a local send-only mail service on a dedicated Ubuntu VM.
Table of Contents
Create a send-only mail server with Postfix
Find your external IP address
Many VMs use NAT to accesss the internet. Their ifconfig output won't match
the actual internet IP that the emails will send from.
To check your external IP address, execute:
dig +short myip.opendns.com @resolver1.opendns.com
Below, the output of this command will be used as <ext_ip>
If you have a static public IP address you can use it as <ext_ip>
Set your hostname to an FQDN in /etc/hosts
This step is only required if you don't already have a local DNS server or internet routed static IP with a valid FQDN.
Lets say that your mail will come from a server named alerts.example.com. Set the hosts file like this:
vi /etc/hosts
127.0.0.1 alerts.example.com
<ext_ip> alerts.example.com
Install Postfix
This is the software that manages your mail queue and handles SMTP.
apt-get install -y postfix mailutils
If it asks you which type of server to install, select Internet Site.
Give it an FQDN when prompted. If you will be sending emails from
[email protected], enter alerts.example.com.
Configure Postfix
Here's a configuration that's worked for me.
Be sure to change the myhostname field.
vi /etc/postfix/main.cf
myhostname = alerts.example.com
smtpd_banner = $myhostname ESMTP $mail_name (Ubuntu)
biff = no
append_dot_mydomain = no
readme_directory = no
smtpd_tls_cert_file = /etc/ssl/certs/ssl-cert-snakeoil.pem
smtpd_tls_key_file = /etc/ssl/private/ssl-cert-snakeoil.key
smtpd_use_tls = yes
smtpd_tls_session_cache_database = btree:${data_directory}/smtpd_scache
smtp_tls_session_cache_database = btree:${data_directory}/smtp_scache
smtpd_relay_restrictions = permit_mynetworks permit_sasl_authenticated defer_unauth_destination
alias_maps = hash:/etc/aliases
alias_database = hash:/etc/aliases
mydestination = $myhostname, 63ec22ec9fc1, localhost.localdomain, , localhost
relayhost =
mynetworks = 127.0.0.0/8 [::ffff:127.0.0.0]/104 [::1]/128
mailbox_size_limit = 0
recipient_delimiter = +
inet_interfaces = loopback-only
inet_protocols = all
Once configured, restart Postfix:
systemctl restart postfix
Send a test email from the command-line
Pipe some stdout to the mail command. This will be used as the body of the email.
echo "Test alert please ignore" | mail \
-a "FROM:[email protected]" \
-s "Test alert" [email protected]
Troubleshooting
Often emails don't go through. There are lots of reasons that can happen.
Check for & remove mail stuck in the queue
Show the mail queue. It might tell you the error if the email is there.
mailq
If you've got a scheduled job that is adding emails, it can fill the queue up and make you look like a spammer. Some mail servers will rate limit a sender, especially if they haven't set up mechanisms by which they can be trusted.
To remove items from the mail queue by ID, run
# If you don't pass <ID> it will delete the all.
postsuper -d <ID>
Outlook is blocking your emails
If you get a 500 error from outlook.*, it could need a connector or a rule exception for the filter. I haven't tested the connector.