Domain Warm-up

After setting up email domain configuration, warm up the domain. This is the next step in improving sender reputation.

Domain warm-up is the gradual increase in the number of emails sent from a new domain to establish trust with mailbox providers (such as Gmail and Outlook) and avoid being flagged as spam.

Reteno automatically warms up the domain for clients who have verified it.

By default, all clients send through a shared IP pool, which is why warm-up and reputation monitoring in Reteno focus on domain-level signals rather than IP-level ones. A dedicated IP is available on request as a paid option — see Dedicated IP Pool.

Before You Start

Reteno supports warm-up for third-level domains, such as mail.company.com, promo.company.com, or news.company.com. You should also check the second-level domain, such as company.com, because other subdomains of this domain may have their own sending history and affect the overall brand reputation with mailbox providers.

Check the following:

• which third-level domain is used for Reteno sends;
• which other subdomains are used for email sending;
• whether there are any SPF, DKIM, or DMARC issues on related domains;
• whether other subdomains are sending large email volumes without warm-up;
• whether related subdomains have any negative sending history.

For what SPF, DKIM, and DMARC do, see How Email Authentication Works.

How Warm-up Works

The example below shows how the process works and how many days a warm-up takes for a target of 100,000 emails per day.

Create an email and launch a campaign:

• First day campaign. On the first day with a new domain, you can send up to 1,000 emails; otherwise, the campaign may raise suspicions on email servers. Reteno sends the first 1,000 emails signed with your DKIM, and the remaining 99,000 with the Reteno domain signature.
• Second day campaign. On the second day, Reteno sends 2,000 emails with your DKIM and 98,000 with the Reteno domain signature, and so on.

Reteno's DKIM signs each campaign regardless of the customer's domain. Initially, most emails are sent with the Reteno signature, and the number of emails sent with your domain signature gradually increases.

When the new domain's warm-up reaches the required level, all emails are sent with two DKIM signatures — yours and Reteno's.

For example, if your target daily sending limit is 100,000 emails, it takes 11 days to complete the domain warm-up.

Dedicated IP Pool

To request a dedicated IP, contact your account manager.

A dedicated pool is assigned per client and can serve several of the client's accounts — you specify which accounts and sending domains use it. Any of them can later be excluded and returned to the shared pool on request, while the others keep sending from the dedicated pool. Dedicated IPs are warmed up from scratch at the standard ramp-up pace; a domain added to the pool later also starts its warm-up from zero, and after the switch the sending speed for those domains is reset to the base level.

Checking the Sending Limit

There are two statuses of the daily sending limit:

• Not reached
• Has been reached/Has been reached for some domains

Go to Settings → Domain verification and click Daily sending limit to view your daily sending limits.

The Sending Limit Has Not Been Reached

Hover over the progress bar next to the domain name, and a tooltip appears showing the number of messages sent and the remaining messages.

The Sending Limit Has Been Reached

Domains that have reached daily limits are displayed in a separate list.

If your domain has no strict DMARC policy, sending limit restrictions are not displayed in your account. In that case, please contact our technical support to get information about warm-up.

Warm-up Under a Strict DMARC Policy

A strict DMARC policy changes how the warm-up limit behaves for you. DMARC itself does not limit how many emails you can send — it tells mailbox providers how to handle messages that fail authentication. During warm-up this matters because emails above the daily limit are signed only with the Reteno DKIM signature.

A message passes DMARC only when at least one mechanism — SPF or DKIM — both passes authentication and aligns with the domain in the visible From address. When neither does, the policy in your DMARC record tells mailbox providers how to treat the message:

• none — monitor authentication without requesting quarantine or rejection,
• quarantine — treat the message as suspicious, usually placing it in the spam folder,
• reject — reject the message.

If the value is set to none, the warm-up proceeds as described above. However, if DMARC is set to quarantine or reject, when the daily limit is reached during the warm-up period, no further emails are sent. Even if the emails are signed using the DKIM signature of the Reteno domain, they may still end up in spam or be rejected. Sending resumes by itself the next day: warm-up data is refreshed at 00:00 UTC, the domain moves to the next day of the schedule, and the higher limit applies from then on. You do not need to ask support to lift the block.

Under a strict DMARC policy, manually limit the number of daily sends during the warm-up period. If you need to temporarily relax the policy, use quarantine rather than none — none removes DMARC monitoring entirely, while quarantine still protects the domain and provides visibility into authentication failures.

Use the MxToolbox service to check DMARC domain settings.

When manually limiting the number of daily sends, use the following recommendations:

1. Begin the campaign with 10–20 emails per send, spaced a few hours apart. This way, approximately a hundred emails will be sent throughout the day.
2. Send the most engaged users. Users should open, read, and take the desired action.
3. Plan the warm-up phase for 4–6 weeks. Typically, the process occurs within this timeframe.
4. Use the Postmaster tools to check domain settings and reputation.

The next step in improving the sender's reputation is setting up double opt-in.

Related Articles

• Setting Up Email Domain Authentication
• How Email Authentication Works
• Email Deliverability: Getting Started Guide
• Monitoring Email Deliverability with Google Postmaster Tools
• Domain Verification Troubleshooting