Enhance email deliverability with a Reverse DNS and SPF record
A PTR (Pointer) record is crucial for a mail server as it establishes a Reverse DNS mapping, verifying the legitimacy of the server's IP address. This record is vital for email deliverability, preventing emails from being flagged as spam during Reverse DNS checks. It contributes to forward-confirmed Reverse DNS (FCrDNS), aligning forward and Reverse DNS entries to enhance server credibility. Servers lacking a valid PTR record may face rejection by other mail servers, impacting deliverability. Overall, a PTR record is a standard best practice, promoting trustworthiness and smooth email communication. Additionally, an SPF (Sender Policy Framework) record is essential for email deliverability, as it specifies authorized mail servers for a domain, preventing email spoofing and further bolstering the authenticity of outgoing emails.
This tutorial will guide you on how to install and configure a mail server and a PTR record using IONOS Cloud DNS API. The steps we will follow are:
Set up a Dedicated Core server in IONOS Cloud.
Create an A and MX record for your mail server.
Install and configure mail server.
Add a Reverse DNS record and SPF record for your mail server.
Test the email deliverability.
Set up a Dedicated Core Server in IONOS Cloud
Note:
The user who creates the server has full root or administrator access rights. A server, once provisioned, retains all its settings (resources, drive allocation, password, and so on), even after server restart at the operating system level.
The server will only be removed from your virtual data center once you delete it in the DCD.
To set up a Dedicated Core server in IONOS Cloud, follow these steps:
1. Create a Dedicated Core server and configure the server in the Settings tab by following the steps in Create a Dedicated Core Server.
2. Configure the server Network settings by following the steps in the Dedicated Core Server network settings.
3. Configure the server Storage settings by following the steps in the Dedicated Core Server storage settings.
4. Continue to provision the changes and start the Dedicated Core Server by following the steps in the Provision changes and starting the Dedicated Core Server.
Result: A Dedicated Core Server is set up and started along with the configuration of Settings, Network, and Storage setup.
Dedicated Core Server network settings
In the DCD > Inspector pane on the right, configure the following network details in the Network tab.
1. Name: Choose a name unique to this Virtual Data Center (VDC).
2. MAC: Assigned on VM creation.
3. LAN: Select the LAN connection that is connected to the internet, by default LAN 1.
4. Firewall: By default, the firewall is disabled. To enable firewall rules, make sure that incoming and outgoing traffic is allowed on port 25 for UDP and TCP.
5. IP Management: To reserve an IP for the server, click IP Management under Management in the top menu bar.
6. Click Reserve IP and a new pop-up window Reserve IP appears. Add a Name, Number of IPs and select a region that is the same as the region of your Dedicated Core server. Click Reserve IP to reserve the IP and confirm the reservation by pressing OK.
7. Exit the IP management window and return to the Network tab of your Dedicated Core Server.
8. In the IPv4 Configuration click Add IP and a select one of your reserved IPs.
Result: The Network settings for a Dedicated Core server are configured.
Dedicated Core Server storage settings
Warning: The storage type cannot be changed after provisioning.
In the DCD > Inspector pane on the right, configure the following storage details in the Storage tab.
1. Click SSD and a new pop-up window Create New Attached Storage appears.
2. Configure the following storage details:
Name: Enter a name that is unique within your VDC.
Availability Zone: Leave on "Auto".
Size in GB: Enter "50" which is sufficient for this tutorial.
Performance: Select "Standard".
Image: You can select one of IONOS images or snapshots, or use your own. For this tutorial, we will use an Ubuntu server image from IONOS. To make the same choice, select ubuntu-22.04-server-cloudimg-amd64 under IONOS Images.
Password: Create a password for the "root" user of the server. You will need this password to SSH and make changes.
SSH Keys: Select an SSH key stored in the SSH Key Manager.
Ad-hoc SSH Key: If you have not created an SSH key, copy and paste the public part of your SSH key into this field.
Cloud-Init user data: Leave on "No configuration".
Boot from Device: Select this checkbox to make the SSD drive bootable.
3. Click Create SSD Storage to create the SSD storage.
Result: The Storage settings for a Dedicated Core server are configured.
Provision changes and start the Dedicated Core Server
1. Select the newly created Dedicated Core server.
2. From the Settings tab in the Inspector pane, select Power > Start.
3. Click Provision Changes in the lower right corner and further click Provision Now.
Result: The Dedicated Core server is provisioned and started.
Next steps: After your changes are provisioned and the server is started, select your Dedicated Core server, click the Network tab in the Inspector pane and copy one of the IPv4 addresses.
Create an A and MX record for your mail server
1. Create an A record for demo-ionos.cloud using IONOS Cloud DNS API:
We already own the zone mail.demo-ionos.cloud
and we will use it for this tutorial. Previously we have created a zone demo-ionos.cloud using IONOS Cloud DNS API. To get more information how to create a zone using IONOS Cloud DNS API, please refer to Create a zone using IONOS Cloud DNS API.
Replace <zone_id> with your zone id.
For more information on how to create a record for a zone using IONOS Cloud DNS API, please refer to Create a record for a zone using IONOS Cloud DNS API. In the above example make sure to use your own <zone_id>
and <your_server_ip>
along with your <authorization token>
.
2. Create an MX record for demo-ionos.cloud using IONOS Cloud DNS API:
For more information on how to create a record for a zone using IONOS Cloud DNS API, please refer to Create a record for a zone using IONOS Cloud DNS API.
Install and configure mail server
1. Connect to your Dedicated Core server via SSH:
and make sure that you are executing the following commands as root.
2. Update the system:
If a kernel is updated it is suggested that you reboot the server.
3. Install Postfix:
Follow the on-screen prompts to configure Postfix. Select Internet Site and enter the domain name of your mail server, in this tutorial we will use our domain mail.demo-ionos.cloud
.
4. Install OpenDKIM:
5. Generate OpenDKIM keys:
Execute the following commands to generate OpenDKIM keys for your domain and move them to the appropriate directory:
Replace mail.demo-ionos.cloud
with your domain name.
6. Edit the OpenDKIM configuration file:
Add or modify the following lines:
Replace mail.demo-ionos.cloud
with your domain name.
7. Install Postfix and Mailutils:
Follow the on-screen prompts to configure Postfix. Select Internet Site and enter the domain name of your mail server, for example, demo-ionos.cloud
.
7. Configure Postfix to use OpenDKIM:
Modify the line containing information about smtp_banner
to include the domain name of your mail server, for example, mail.demo-ionos.cloud
. The line should look like this:
and add the following lines at the end of the file:
and the complete /etc/postfix/main.cf
file looks like this:
8. Restart services:
9. Test the configuration:
Replace <your-email>@<your-domain>
with your email address.
In your mailbox you should receive an email with the subject "Test Email" and the body "This is a test email" but it might be in the spam folder, depending on your email provider. In our case the email was in the spam folder with a note "Mail system could not verify that demo-ionos.cloud actually sent this message (and not a spammer)."
10. Check the mail log:
Add a Reverse DNS record and SPF record for your mail server
1. Create a PTR record for your mail server using IONOS Cloud DNS API:
2. Create an SPF record for mail.demo-ionos.cloud
using IONOS Cloud DNS API:
For your SPF record make sure that instead of mail.demo-ionos.cloud
you use your own domain name.
After creating the PTR record and the SPF record, it might take around 10 minutes to propagate.
3. Test again the email deliverability:
Replace <your-email>@<your-domain>
with your email address.
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