Is warm-up necessary for a new subdomain if the IP is already warm?

Yes, a warm-up is still necessary. While your IP address might have a good reputation, mailbox providers (like Outlook ) primarily assess sender reputation at the subdomain level. A new subdomain needs to build its own sending history and trust.

How long does a subdomain warm-up take when the IP is already warmed?

The warm-up period for a new subdomain on an already warmed IP is typically shorter than a full IP warm-up. It can range from a few days to a few weeks, depending on your target sending volume and list engagement. You can be more aggressive with volume increases compared to a cold IP, but still need to be gradual.

Which contacts should I send to first during a new subdomain warm-up?

Start by sending to your most engaged subscribers, such as those who have recently opened or clicked your emails. These positive interactions help build a good reputation for the new subdomain quickly. Avoid sending to inactive or old contacts during the initial warm-up phase.

Do I need to set up SPF, DKIM, and DMARC for a new subdomain?

Yes, ensure your SPF, DKIM, and DMARC records are correctly configured for the new subdomain. These authentication protocols are crucial for verifying your sending legitimacy and preventing your emails from being flagged as spam.

How can I monitor the success of my subdomain warm-up?

Monitor your open rates, click-through rates, bounce rates, and complaint rates. Use Google Postmaster Tools and your ESP's analytics. Also, regularly check if your subdomain or IP is listed on any email blocklists or blacklists .

When switching to a new subdomain for email, what warm-up process is required? - Sender reputation - Email deliverability - Knowledge base

Many businesses consider switching to a new subdomain for email sending, often to segment their email types (e.g., transactional versus marketing) or to isolate potential deliverability issues. A common question arises: if my primary domain (or root domain) and its associated IP address already have a strong sender reputation, do I still need to warm up a new subdomain on that same, warmed IP?

The short answer is yes, a warm-up process is still required. Even if your main domain is well-established, internet service providers (ISPs) and mailbox providers primarily assess reputation at the subdomain level. While an existing warmed IP helps, the subdomain itself is seen as a new sender that needs to build its own trust.

This guide will walk through the essential steps for warming up a new email subdomain, even when your IP is already warm. Understanding this process is key to ensuring your emails consistently land in the inbox and avoid spam folders.

Why subdomain warm-up matters

Mailbox providers, such as

Gmail and

Yahoo, assess sender reputation based on multiple factors, and the sending subdomain is a primary identifier. Each subdomain builds its own unique sending history, engagement metrics, and complaint rates. Even if the root domain, for example, brand.com, has an excellent reputation, a new subdomain like e.brand.com starts with a neutral, unestablished reputation. Sending high volumes instantly from a new subdomain, even on a warm IP, signals suspicious behavior to ISPs, leading to messages being routed to spam folders or even blocked.

The separation of reputation is precisely why many senders choose to use subdomains. For instance, you might use marketing.yourdomain.com for promotional emails and transactional.yourdomain.com for order confirmations or password resets. This strategy helps protect the reputation of your critical transactional emails from the potentially more fluctuating reputation of marketing sends. Because the reputation is distinct, each new subdomain requires its own warm-up.

While the domain reputation is key, the IP address also plays a role. A dedicated, pre-warmed IP can shorten the overall subdomain warm-up period. However, this doesn't eliminate the need for warming. The ISP still needs to see consistent, positive sending behavior associated directly with the new subdomain.

Essential steps for subdomain warm-up

Before you start sending from your new subdomain, proper authentication is non-negotiable. This includes setting up SPF, DKIM, and DMARC records for the specific subdomain. These protocols verify that your emails are legitimate and prevent spoofing. Without them, your emails are highly likely to land in the spam folder, regardless of your warm-up efforts. If you're migrating to a new ESP, ensure these are correctly configured for the new subdomain.

DNS records for email authentication

Ensure your DNS records are correctly configured for your new subdomain, which is critical for establishing trust with mailbox providers.

SPF Record: Specifies which mail servers are authorized to send email on behalf of your subdomain.
DKIM Record: Adds a digital signature to your emails, allowing recipients to verify that the email was not altered in transit.
DMARC Record: Tells receivers what to do if an email fails SPF or DKIM authentication.

Example DNS records for e.brand.comDNS

e.brand.com. IN TXT "v=spf1 include:_spf.example.com ~all"
selector1._domainkey.e.brand.com. IN TXT "v=DKIM1; p=MIGfMA0GCSqG..."
_dmarc.e.brand.com. IN TXT "v=DMARC1; p=none; rua=mailto:reports@yourdomain.com"

The core of any warm-up is gradually increasing your sending volume. You cannot simply switch all your email traffic to a new subdomain overnight, even if the IP is already warm. This sudden burst of volume from an unknown sender (the new subdomain) will likely trigger spam filters.

Start with a small volume of highly engaged recipients. These are contacts who frequently open your emails, click links, and interact positively. Their positive engagement signals to ISPs that your emails are desired and valuable. Gradually increase the volume each day, or every few days, monitoring your deliverability closely. A sample warm-up schedule often starts with hundreds of emails and slowly ramps up over several weeks, depending on your target volume. For more on this, this guide on how to warm up a domain provides a detailed schedule example.

IP warm-up

Focus: Building a reputation for the IP address itself, establishing it as a trustworthy source of email.
Duration: Typically weeks, or even months for very high volumes.
Volume: Starts very low (hundreds) and increases slowly.

Subdomain warm-up (on warmed IP)

Focus: Building a unique reputation for the new subdomain within the context of an already trusted IP.
Duration: Typically shorter, a few days to a few weeks, depending on volume.
Volume: Can be more aggressive than IP warming, but still gradual.

Monitoring and maintaining reputation

Throughout the warm-up, continuous monitoring is critical. Pay close attention to your deliverability metrics, including open rates, click-through rates, bounce rates, and crucially, complaint rates. A sudden spike in bounces or complaints indicates that you are increasing volume too quickly or sending to unengaged recipients. If this happens, reduce your sending volume immediately and re-evaluate your strategy. Services like Mailgun's guide on domain warm-up also emphasizes the importance of continuous monitoring.

Check major email blocklists (or blacklists) regularly. Getting listed on a blocklist or blacklist, even a minor one, can severely impact your deliverability. If you find your new subdomain or associated IP on a blocklist, cease sending immediately, identify the cause, and work to get delisted. Maintaining a clean list and engaging content helps prevent this. You can learn more about what happens when your domain is blocklisted in our in-depth guide.

The content you send during warm-up should be highly engaging and relevant to your audience. Avoid anything that could be perceived as spammy, such as excessive images, suspicious links, or aggressive sales language. Keep your email list clean by regularly removing unengaged or invalid addresses. A high bounce rate from sending to old or bad contacts can also hurt your new subdomain’s reputation.

Views from the trenches

Best practices

Always set up SPF, DKIM, and DMARC for the new subdomain before sending any emails.

Begin with your most engaged subscribers who are likely to open and click your emails.

Monitor key metrics like opens, clicks, bounces, and complaints daily.

Adjust your sending volume based on performance; slow down if you see negative trends.

Maintain a consistent sending schedule during the warm-up period.

Common pitfalls

Sending high volumes too quickly, even on a warmed IP, can lead to blocklisting.

Neglecting to set up proper email authentication (SPF, DKIM, DMARC) for the subdomain.

Sending to unengaged or old lists, resulting in low engagement and high complaints.

Ignoring early warning signs from deliverability metrics or blocklist notifications.

Expecting the same immediate deliverability as a fully warmed root domain.

Expert tips

Even with a warmed IP, a new subdomain needs its own reputation building, though it may be faster.

Use transactional or highly engaged marketing emails for initial warm-up sends.

Consistency in volume and content type helps ISPs build trust faster.

Consider segmenting your audience and sending smaller, targeted batches during the ramp-up.

If deliverability issues arise, reduce volume and review email content and list quality.

Expert view

Expert from Email Geeks says that subdomains have different reputations from each other, even when using the same IP.

2020-05-20 - Email Geeks

Expert view

Expert from Email Geeks says that if the IPs are the same, the warm-up period for the new subdomain will likely be shorter.

2020-05-20 - Email Geeks

Key takeaways

Ensuring successful email delivery from a new subdomain, even when your IP is already warm, requires a deliberate and strategic warm-up process. While a pre-warmed IP can shorten the overall timeline, the new subdomain still needs to establish its own sender reputation with mailbox providers.

By correctly configuring authentication (SPF, DKIM, DMARC), starting with highly engaged contacts, gradually increasing your sending volume, and diligently monitoring your deliverability metrics, you can build a strong reputation for your new subdomain. This methodical approach will help ensure your emails bypass spam filters and consistently reach your subscribers' inboxes.

Remember, email deliverability is an ongoing process. Consistent monitoring and adherence to best practices, such as maintaining a clean list and sending relevant content, are essential for long-term success on any sending domain or subdomain.