How to Send Emails Using SMTP Relay with Azure Communication Services

How to Send Emails Using SMTP Relay with Azure Communication Services. This tutorial covers setting up Azure Communication Services to send emails via SMTP relay, perfect for developers, IT admins, and cloud technicians. A step-by-step guide for developers and IT admins to configure secure email delivery from apps, printers, and IoT devices.

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Why Use Azure SMTP Relay?

Avoid IP blacklisting by relaying through Microsoft’s trusted servers
No mail server maintenance – fully cloud-based solution
Enterprise-grade security with TLS encryption and authentication
Scalable pricing – pay only for emails sent

Use Cases

Sending emails from applications (CRM, ERP)
Configuring “scan to email” on printers
Sending emails from IoT devices or backend systems

Benefits of Azure SMTP Relay

Avoids IP blacklisting by relaying through trusted SMTP server
Secure and authenticated email delivery
No need to host your own mail server

Prerequisites for Azure SMTP Relay

Azure subscription (Pay-As-You-Go works)
Communication Service resource in Azure
Verified domain (or subdomain) for email
SMTP client/app/code to send emails
Open outbound ports (587 recommended, or 25)

Step-by-Step Setup to Send Emails Using SMTP Relay

1. Create Email Communication Service in Azure

Search for “Email Communication Services” in Azure portal
Create new resource:
- Resource group: “Email-SMTP-Relay”
- Location: Choose nearest region
- Name: “Email-SMTP-Relay”
- Data location: Select appropriate region

2. Verify Your Domain for SMTP Relay

Create a subdomain (e.g., newsletters.yourdomain.com)
In Email Communication Service:
- Add custom domain (newsletters.yourdomain.com)
- Verify domain by adding TXT record to DNS
- Configure SPF and DKIM records (TXT and CNAME records)

Important Note: When adding DKIM records for subdomains, append your subdomain to the Azure-provided domain key (e.g., add “.newsletters” to the domain key value).

3. Create Communication Service

Search for “Communication Services” in Azure portal
Create new resource:
- Name: “Newsletter-Service”
- Same resource group as before
- Same location

4. Connect Domain to Communication Service

In Communication Service, go to “Connect your email domains”
Select your Email Communication Service resource
Select your verified domain

5. Set Up Authentication

Create Azure AD application:
- In Azure AD > App registrations > New registration
- Name: “Newsletter-Delivery-App”
- Accounts in this organization only
- Register
Create client secret:
- Go to Certificates & secrets
- New client secret (e.g., “Delivery-App-Secret”)
- Copy the secret value (this will be your SMTP password)
Assign role:
- In Communication Service > Access Control (IAM)
- Add role assignment: “Communication Email Service Owner”
- Select your “Newsletter-Delivery-App” as member

6. Create SMTP Usernames

In Communication Service > SMTP usernames
Add username (e.g., “newsletters” or “newsletter-delivery@newsletters.yourdomain.com“)

7. Configure Mail From Addresses

In Domains > your domain > Mail from addresses
Default addresses are created (e.g., donotreply@newsletters.yourdomain.com)
To add more addresses, use Azure CLI:

az communication email domain sender-username create \
  --domain-name newsletters.yourdomain.com \
  --email-service-name Email-SMTP-Relay \
  --resource-group Email-SMTP-Relay \
  --sender-username scanner21 \
  --display-name "Scanner 21"

Sending Emails

$SMTPServer = "smtp.azurecomm.net"
$SMTPPort = 587  # or 25
$Username = "newsletters"  # or your SMTP username
$Password = "your-client-secret-value"  # from Azure AD app
$From = "donotreply@newsletters.yourdomain.com"
$To = "recipient@example.com"

$Subject = "Test Email"
$Body = "This is a test email using Azure Communication Services SMTP relay"

$SMTPMessage = New-Object System.Net.Mail.MailMessage($From, $To, $Subject, $Body)
$SMTPClient = New-Object Net.Mail.SmtpClient($SMTPServer, $SMTPPort)
$SMTPClient.EnableSsl = $true
$SMTPClient.Credentials = New-Object System.Net.NetworkCredential($Username, $Password)
$SMTPClient.Send($SMTPMessage)

Troubleshooting

If emails aren’t sending, check:
- Outbound port 587/25 is open in firewall
- Domain verification is complete (may take 15-20 minutes)
- Newly created sender addresses may take time to activate
- TLS must be enabled when using port 25