Deploying a Non-Google SMTP RelayHost with Asterisk

Why Do You Need a RelayHost? Many Internet Service Providers (ISPs) block downstream mail servers from sending email to reduce spam. If you have a PBX sitting behind a Comcast cable modem and you don’t have a business account, that would be you.

What Is a RelayHost? A RelayHost is an intermediate mail provider that provides last mile delivery of your server’s outbound email without your having to worry about the intricacies of setting up and properly configuring an SMTP gateway. Instead, your server pushes your outbound email messages to the smarthost using your credentials and leaves the rest of the delivery task to the RelayHost.

Choosing a RelayHost. Lucky for all of us, there are many RelayHost providers from which to choose. Most offer a free tier with 100 or more daily emails. For most PBXs, that is more than ample without spending a dime. If your server pushes out more than 100 emails a day, then there are commercial tiers of service available from these same providers. Here are some of the favorites recommended by our users: Twilio’s SendGrid, Mailjet, SendInBlue, and our own free MXroute offering. We would prefer you use our service as a last resort if you can’t get any of the other free offerings to work. We’ll show you how to set up Twilio’s SendGrid as a RelayHost to get you started.

Configuring a RelayHost with Incredible PBX. There’s good news and bad news. While all of these solutions offer a free tier, the setup process with some of these services can be a bear. We’ve attempted to take the pain out of this by walking you through the setup steps. For openers, configuring SendMail as an SMTP Smarthost is not for mere mortals so we’ll first migrate your PBX to Postfix to simplify the setup procedure. Here is a quick list of the tasks:

1. Migrate Your PBX from SendMail to Postfix
2. Obtain an Account with SmartHost Provider
3. Configure Postfix Email Relay Using SmartHost Provider
4. Test Outbound Mail

Migrating Incredible PBX 2022 to Postfix. Our new Incredible PBX 2022 build for Rocky 8 comes with both SendMail and Postfix preinstalled. So it’s simple to switch gears. Here are the commands:

systemctl stop sendmail
systemctl disable sendmail
systemctl start postfix
systemctl enable postfix
sed -i 's|-c sendmail|-c postfix|' /usr/local/sbin/pbxstatus
sed -i 's|SendMail| Postfix|' /usr/local/sbin/pbxstatus
systemctl status postfix

Migrating Incredible PBX 2021 to Postfix. By default, Incredible PBX 2021 servers do not include Postfix. So here are the steps to install Postfix and remove SendMail. These steps also apply to all releases of Incredible PBX on the Raspbian platform.

apt-get update
apt-get install postfix sasl2-bin -y
# choose No Configuration option when prompted in:
# dpkg-reconfigure postfix
systemctl stop sendmail
systemctl disable sendmail
systemctl start postfix
systemctl enable postfix
sed -i 's|-c sendmail|-c postfix|' /usr/local/sbin/pbxstatus
echo "incrediblepbx.com" > /etc/mailname
sed -i 's|SendMail| Postfix|' /usr/local/sbin/pbxstatus
systemctl status postfix

Creating a Free SendGrid Account. Begin by navigating to the SendGrid Start for Free link. Enter your Email Address and a 16-character password of your choice. Accept the Terms of Service and click Create Account. Fill in the Personal Information and click Get Started. Create a Single Sender Identity. Confirm receipt of the verification email. You can skip enabling Two-Factor Authentication if desired. Next, open the Email API tab and click Integration Guide. Choose SMTP Relay and create an APIKEY. Copy the generated APIKEY to a safe place. It cannot be deciphered again!

Now edit /etc/postfix/main.cf and add the following entries to the bottom of the file:

smtp_sasl_auth_enable = yes
smtp_sasl_password_maps = hash:/etc/postfix/sasl_passwd
smtp_sasl_security_options = noanonymous
smtp_sasl_tls_security_options = noanonymous
smtp_tls_security_level = encrypt
header_size_limit = 4096000
relayhost = [smtp.sendgrid.net]:587

Then create /etc/postfix/sasl_passwd and enter the following, replacing YOUR-APIKEY with your actual key from above:

[smtp.sendgrid.net]:587 apikey:YOUR-APIKEY

Complete the setup by issuing the following commands:

chmod 600 /etc/postfix/sasl_passwd
postmap /etc/postfix/sasl_passwd
systemctl restart postfix
systemctl status postfix

IMPORTANT NOTE: With SendGrid, the email address you entered for your Single Sender Identity must match the FROM: address on every outbound email message sent from your server. We’ll need to adjust the FROM: address in FreePBX before any voicemail emails can be successfully sent. Also, if you send emails from the command line, the syntax must be as shown here with your sender@yourdomain.com matching what was entered as your Sender Identity email address.

echo "test" | mail -r sender@yourdomain.com -s testmessage recipient@somedomain.com

At least with Gmail recipients, they may also see the following with messages from your PBX until they click Looks Safe:

Finally, be sure to adjust the FROM address for outbound voicemail messages in the FreePBX GUI. Login as admin and enter your Sender Identity Email Address in the Server Email field in Settings -> Voicemail Admin -> Settings -> Email Config.

You can check for errors by reviewing the Postfix mail log: tail /var/log/mail.log.

UPDATE: Setup scripts for Debian 10 and Rocky 8 can be downloaded here.

Originally published: Thursday, March 17, 2022

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