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This guide walks you through adding the required DNS records for Lettr using IONOS’s DNS management. IONOS is a web hosting and domain provider that offers DNS hosting for domains managed through its IONOS Control Panel. You will configure a sending domain (CNAME, DKIM TXT, and DMARC TXT records) and, optionally, an inbound domain (MX records), tracking domain (two CNAME records), and storage domain (CNAME and two TXT records).

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Sending Domain Setup

A sending domain authenticates your outgoing emails with DKIM and DMARC, ensuring they are delivered reliably and not marked as spam. This requires a CNAME record for domain verification, a TXT record for DKIM signing, and a TXT record for DMARC policy. To create a sending domain in Lettr:
  1. Select Domains in the navigation panel
  2. Select Sending Domains
  3. Click Create Sending Domain
  4. Enter your desired sending subdomain (e.g. mailing.company.com)
  5. Click Create Domain
Use a subdomain (e.g. mailing.company.com) instead of the root domain (company.com). A subdomain provides proper reputation segmentation and is required if you also plan to receive emails with Lettr.
Click your new domain in the Sending Domains list. This will display a list of DNS records that need to be configured. Keep this page open — you will need these values soon.

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Configure IONOS DNS

Log in to the IONOS Control Panel and click the Domains & SSL tile on the dashboard. Find the domain you want to configure, click the three-dot menu in the Actions column next to it, and select DNS.
If your domain was purchased through IONOS or your nameservers already point to IONOS, skip nameserver configuration entirely. Your domain is already using IONOS’s nameservers by default — proceed directly to adding the DNS records below.
If you registered your domain elsewhere but want to manage DNS on IONOS, you must first update the nameservers at your registrar to the IONOS nameservers shown in your domain’s DNS settings. IONOS assigns four nameservers per account in the format ns1045.ui-dns.org, ns1045.ui-dns.de, ns1045.ui-dns.biz, and ns1045.ui-dns.com — the number prefix (e.g. 1045) varies by account. Use the exact values shown in your IONOS control panel.
Until the nameservers are updated, any records you add in IONOS will not resolve.

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Add CNAME Record

The CNAME record verifies domain ownership with Lettr’s email infrastructure. Copy the CNAME values from Lettr to IONOS:
  1. Click Add record in the DNS management page.
  2. Select CNAME from the record type dropdown.
  3. Set Hostname to the Hostname value from Lettr (without your domain suffix). For example, paste only mailing.
  4. Set Point to to the Value from Lettr.
  5. Leave TTL at the default (3600).
  6. Click Save.
IONOS automatically appends your domain to the hostname. Always paste only the subdomain portion (e.g. mailing, not mailing.company.com). If you paste the full hostname, the resulting record will resolve as mailing.company.com.company.com, which will fail verification.

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Add TXT Record (DKIM)

The DKIM record adds a cryptographic signature to your outgoing emails, allowing recipients to verify they were sent by an authorized sender. Copy the TXT values from Lettr to IONOS:
  1. Click Add record in the DNS management page.
  2. Select TXT from the record type dropdown.
  3. Set Host name to the Hostname value from Lettr (without your domain suffix). For example, paste only scph0126._domainkey.mailing.
  4. Set Value to the Value from Lettr.
  5. Leave TTL at the default (3600).
  6. Click Save.
IONOS automatically appends your domain to the hostname. Always paste only the subdomain portion (e.g. scph0126._domainkey.mailing, not scph0126._domainkey.mailing.company.com).

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Add TXT Record (DMARC)

The DMARC record tells receiving mail servers how to handle emails that fail authentication checks, protecting your domain from spoofing. Copy the TXT values from Lettr to IONOS:
  1. Click Add record in the DNS management page.
  2. Select TXT from the record type dropdown.
  3. Set Host name to the Hostname value from Lettr (without your domain suffix). For example, paste only _dmarc.mailing.
  4. Set Value to the Value from Lettr (e.g. v=DMARC1;p=none;).
  5. Leave TTL at the default (3600).
  6. Click Save.
IONOS automatically appends your domain to the hostname. Always paste only the subdomain portion (e.g. _dmarc.mailing, not _dmarc.mailing.company.com).

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Verify Your Sending Domain

After adding all three DNS records, go back to Lettr and click Verify DNS Records. DNS changes on IONOS propagate within about 1 hour in most cases, though external resolvers may take longer.

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Inbound Domain Setup

An inbound domain allows Lettr to receive emails on your behalf. This requires three MX records that direct incoming mail to Lettr’s mail servers.

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Add Inbound Domain to Lettr

To create an Inbound domain in Lettr:
  1. Select Domains in the navigation panel
  2. Select Inbound Domains
  3. Click Create Inbound Domain
  4. Enter your desired inbound subdomain (e.g. inbound.company.com)
  5. Click Create Domain.
Click on your new domain in the Inbound Domains list. This will display the MX records that need to be configured.

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Add MX Records

MX records tell other mail servers where to deliver emails addressed to your domain. Copy the MX values from Lettr to IONOS:
  1. Click Add record in the DNS management page.
  2. Select MX from the record type dropdown.
  3. Set Host name to the Hostname value from Lettr (without your domain suffix). For example, paste only inbound.
  4. Set Points to to rx1.sparkpostmail.com.
  5. Set Priority to 10.
  6. Leave TTL at the default (3600).
  7. Click Save.
  8. Repeat this process for the second (rx2.sparkpostmail.com) and third (rx3.sparkpostmail.com) MX records, each with priority 10.
IONOS automatically appends your domain to the hostname. Always paste only the subdomain portion (e.g. inbound, not inbound.company.com).
All emails sent to the domain or subdomain where MX records are configured will be routed to Lettr. Use a dedicated subdomain (e.g. inbound.company.com) to avoid affecting your primary email.

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Verify Your Inbound Domain

After adding all three MX records, go back to Lettr and click Verify DNS Records. DNS changes on IONOS propagate within about 1 hour in most cases, though external resolvers may take longer.

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Tracking Domain Setup

A tracking domain allows Lettr to track email opens and link clicks using your own custom domain instead of the default Lettr tracking domain. This requires two CNAME records: one for the SSL certificate and one for routing tracking traffic to Lettr’s infrastructure.

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Add Tracking Domain to Lettr

To create a Tracking domain in Lettr:
  1. Select Domains in the navigation panel
  2. Select Tracking Domains
  3. Click Create Tracking Domain
  4. Enter your desired tracking subdomain (e.g. tracking.company.com)
  5. Click Create Domain
Click on your new domain in the Tracking Domains list. This will display the CNAME records that need to be configured.

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Add SSL Certificate CNAME Record

The SSL Certificate CNAME record provisions an SSL certificate for your custom tracking domain, enabling secure HTTPS connections for tracked links. Add the record in IONOS:
  1. Click Add record in the DNS management page.
  2. Select CNAME from the record type dropdown.
  3. Set Hostname to the Hostname from Lettr (without your domain suffix).
  4. Set Point to to the Value from Lettr.
  5. Leave TTL at the default (3600).
  6. Click Save.
IONOS automatically appends your domain to the hostname. Always paste only the subdomain portion (e.g. tracking, not tracking.company.com).

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Add Traffic CNAME Record

The Traffic CNAME record routes click and open tracking requests from your custom domain to Lettr’s tracking servers. Add the record in IONOS:
  1. Click Add record in the DNS management page.
  2. Select CNAME from the record type dropdown.
  3. Set Hostname to the Hostname from Lettr (without your domain suffix).
  4. Set Point to to the Value from Lettr.
  5. Leave TTL at the default (3600).
  6. Click Save.
IONOS automatically appends your domain to the hostname. Always paste only the subdomain portion (e.g. tracking, not tracking.company.com).

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Verify Your Tracking Domain

After adding both CNAME records, go back to Lettr and click Verify DNS Records.

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Storage Domain Setup

A storage domain lets you serve email assets (images, attachments) from your own custom domain instead of the default Lettr storage URL. This requires two TXT records for certificate validation and ownership verification, and a CNAME record for routing asset requests to Lettr’s storage infrastructure.

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Add Storage Domain to Lettr

To create a Storage domain in Lettr:
  1. Select Domains in the navigation panel
  2. Select Storage Domains
  3. Click Create Storage Domain
  4. Enter your desired storage subdomain (e.g. assets.company.com)
  5. Click Create Domain
Click on your new domain in the Storage Domains list. This will display the TXT and CNAME records that need to be configured.

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Add TXT Record (Certificate Validation)

The Certificate Validation TXT record provisions an SSL certificate for your custom storage domain, enabling secure HTTPS delivery of email assets. Add the record in IONOS:
  1. Click Add record in the DNS management page.
  2. Select TXT from the record type dropdown.
  3. Set Host name to the Hostname from Lettr (without your domain suffix).
  4. Set Value to the Value from Lettr.
  5. Leave TTL at the default (3600).
  6. Click Save.
IONOS automatically appends your domain to the hostname. Always paste only the subdomain portion, just as with the CNAME record above.

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Add TXT Record (Hostname Pre-validation)

The Hostname Pre-validation TXT record verifies ownership of the storage domain before Lettr provisions a custom hostname for it. Add the record in IONOS:
  1. Click Add record in the DNS management page.
  2. Select TXT from the record type dropdown.
  3. Set Host name to the Hostname from Lettr (without your domain suffix).
  4. Set Value to the Value from Lettr.
  5. Leave TTL at the default (3600).
  6. Click Save.
IONOS automatically appends your domain to the hostname. Always paste only the subdomain portion, just as with the CNAME record above.

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Add CNAME Record (Domain Routing)

The Domain Routing CNAME record routes asset requests from your custom domain to Lettr’s storage infrastructure. Add the record in IONOS:
  1. Click Add record in the DNS management page.
  2. Select CNAME from the record type dropdown.
  3. Set Hostname to the Hostname from Lettr (without your domain suffix).
  4. Set Point to to the Value from Lettr.
  5. Leave TTL at the default (3600).
  6. Click Save.
IONOS automatically appends your domain to the hostname. Always paste only the subdomain portion (e.g. assets, not assets.company.com).

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Verify Your Storage Domain

After adding all three records, go back to Lettr and click Verify DNS Records.

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Troubleshooting

IONOS automatically appends your domain to the Hostname / Host name field. If you paste the full hostname (e.g. mailing.company.com), the resulting record will resolve as mailing.company.com.company.com, which will fail verification.Always paste only the subdomain portion (e.g. mailing, scph0126._domainkey.mailing, _dmarc.mailing).
IONOS applies DNS changes immediately on their side, but external resolvers may take up to 1 hour to pick up the changes (and in rare cases, ISPs with long cache times may take longer). If verification fails after adding records, check the following:
  • Wait at least 1 hour before your first verification attempt.
  • Confirm the records exist using command-line tools:
# Check CNAME record
dig CNAME mailing.yourdomain.com +short

# Check DKIM record
dig TXT scph0126._domainkey.mailing.yourdomain.com +short

# Check DMARC record
dig TXT _dmarc.mailing.yourdomain.com +short

# Check MX records (inbound)
dig MX inbound.yourdomain.com +short

# Check tracking domain CNAME
dig CNAME track.yourdomain.com +short

# Check storage domain CNAME
dig CNAME assets.yourdomain.com +short
  • Use a web tool like dnschecker.org to verify propagation across multiple DNS servers worldwide.
If your records are saved in IONOS but not resolving, confirm that your domain is using IONOS’s nameservers. You can check this with:
dig NS yourdomain.com +short
The output should include IONOS nameservers in the format ns####.ui-dns.org, ns####.ui-dns.de, ns####.ui-dns.biz, and ns####.ui-dns.com (where #### is a number unique to your account). Your exact nameservers are shown in the IONOS Control Panel under Domains & SSL → your domain’s DNS settings. If the output shows a different provider’s nameservers, update them at your domain registrar.
IONOS does not allow CNAME records at the root of a domain (e.g. company.com). You must use a subdomain for your sending domain (e.g. mailing.company.com). This is also a DNS protocol limitation — CNAME records cannot coexist with other record types at the same name.
If you have IONOS-hosted services active on your domain (e.g. Microsoft 365, IONOS webmail, WordPress hosting), IONOS manages some DNS records automatically. Adding records that conflict with service-managed entries may cause errors or silent overwrites. Check for existing A, CNAME, or MX records on the same hostname before adding new ones, and remove any conflicting entries first.
A common mistake is selecting the wrong type from the record type dropdown:
RecordCorrect Type
Sending verificationCNAME
DKIMTXT
DMARCTXT
Inbound mailMX
Tracking SSL certificateCNAME
Tracking trafficCNAME
Storage certificate validationTXT
Storage hostname pre-validationTXT
Storage domain routingCNAME
The DKIM TXT value is a long string. After saving the record, re-open the DNS management page and confirm the full value is displayed. If it appears truncated, delete the record and re-add it, pasting the full value carefully into the Value field.If IONOS rejects the value due to length, try splitting the p= portion into two quoted strings separated by a space: "v=DKIM1; k=rsa; p=firsthalf" "secondhalf". Paste both quoted strings together into the Value field.
If your DNS records are correctly configured (confirmed with dig or dnschecker.org) and verification still fails after 48 hours, contact Lettr support at support@lettr.com or through the in-app chat. Include your domain name and the output of the dig commands above.

Sending Domains

Learn about sending domain setup, SPF, DKIM, and DMARC.

Inbound Domains

Configure MX records to receive emails with Lettr.

Tracking Domains

Set up a custom tracking domain for click and open tracking.

Storage Domains

Serve email assets from your own custom domain.

Domains Overview

Understand domain types and how they work in Lettr.

Domain Verification Failures

Troubleshoot common DNS configuration and propagation issues.