Summary
Warming up a subdomain for email sending is a critical step in maintaining or improving your email deliverability. While existing IP reputation can offer some advantages, a new subdomain often needs its own reputation built with mailbox providers. The process involves gradually increasing email volume, ensuring proper authentication, and monitoring engagement to demonstrate legitimate sending practices.
Key findings
- Subdomain reputation: Mailbox providers, such as Google, can treat subdomains independently from the root domain, assigning unique reputation scores.
- IP reputation influence: While a new subdomain requires warming, the existing, good reputation of your sending IPs can positively influence the warm-up process, making it smoother than warming a completely cold domain or IP.
- Gradual volume increase: The core of subdomain warm-up involves starting with a low volume of emails and gradually increasing it over time. This mimics organic sending patterns and builds trust with internet service providers (ISPs).
- Authentication importance: Proper configuration of email authentication protocols like SPF, DKIM, and DMARC for the new subdomain is non-negotiable for establishing trust and deliverability.
- Content quality: Sending valuable, engaging content is key to eliciting positive recipient reactions (opens, clicks), which in turn boosts sender reputation.
Key considerations
- Receiver-dependent outcomes: The exact impact and required warm-up intensity can vary depending on the specific receiving mailbox provider. Some may weigh root domain reputation more heavily than others.
- Domain reputation bleed: Negative activity on sibling subdomains or even the parent domain can sometimes affect the deliverability of your new subdomain, even if it has a good score in Google Postmaster Tools.
- Testing strategy: It's advisable to perform small-scale tests with a percentage of your traffic, keeping the existing DKIM configuration, to assess the new subdomain's performance.
- DKIM configuration: Consider implementing the new subdomain as an additional DKIM signature to gradually build its reputation without disrupting the main mail stream. For more on this, see best practices for warming up a new subdomain.
- Monitoring tools: Leverage tools like Google Postmaster Tools (GPT) to monitor your subdomain's reputation. Also, understanding why domain warm-up is important can provide further insights. You may also want to monitor your email domain reputation.
What email marketers say
Email marketers often debate the extent to which existing IP or root domain reputation benefits a new subdomain's warm-up. While some believe it significantly smooths the transition, others emphasize that subdomains are frequently treated as distinct entities by major mailbox providers, necessitating a dedicated warm-up strategy. Many advocate for a gradual volume increase combined with vigilant monitoring of key performance indicators.
Key opinions
- Leveraging IP reputation: Many marketers believe that a strong existing IP reputation will carry a new subdomain through the initial sending phases.
- Gradual domain change: A common approach is to gradually shift email volume from the main domain to the subdomain while utilizing all existing warmed IPs.
- Subdomain independence: Some marketers report that even if the root domain has a good reputation, subdomains can be treated as separate entities by ISPs (like Google), requiring a fresh warm-up.
- Quicker warm-up: There's a general consensus that warming a subdomain can be faster than a completely new domain, largely due to the association with the already reputable parent domain.
Key considerations
- Warm-up similarity to new domains: Marketers often ask if subdomain warming is identical to warming a new, cold domain. The consensus is that while it needs attention, it often gets a head start due to existing reputation.
- Volume scaling for warmed IPs: If existing warmed IPs are used, the daily sending volume for the new subdomain might be able to scale up more aggressively than with truly cold IPs. Consider warming a domain on an existing IP.
- Strategic subdomain use: It's often recommended to use a unique subdomain for email sending that isn't used for other purposes, to isolate its reputation and ensure better deliverability. For more, see our guide on warming up a new subdomain.
Marketer view
Marketer from Email Geeks suggests starting a gradual transition, advising that given good IP reputation, gradually changing the domain while using all existing IPs is a practical approach. This focuses the warm-up effort on the domain itself rather than the IPs.
Marketer view
Marketer from Email Geeks notes that warm-up can be quicker for subdomains, stating that they suspect it is possible to warm up rather quickly since it's still the same domain. This implies a perceived advantage over completely new domains.
What the experts say
Experts concur that while IP reputation provides a foundation, new subdomains require their own distinct warm-up process to build reputation with mailbox providers. This is because ISPs often evaluate subdomains independently. The key is to demonstrate consistent, positive sending behavior, gradually increasing volume, and ensuring all authentication standards are met.
Key opinions
- Independent reputation building: Subdomains will build their own unique sending reputation, even when associated with a well-established root domain or warmed IPs.
- Parent domain influence: The reputation of the parent domain and sibling subdomains can still influence the deliverability of a new subdomain, sometimes leading to 'bleed-across' issues if reputation is poor.
- Strategic DKIM implementation: Introducing the new subdomain as an additional DKIM signature during the transition can help build its reputation more smoothly without disrupting current mail streams.
- Importance of engagement: High user engagement (opens, clicks, replies) is crucial for signaling positive sending practices to ISPs, especially during the initial warm-up phase.
Key considerations
- Careful volume increments: A gradual, measured increase in sending volume is vital to mimic organic growth and avoid being flagged as suspicious. This is similar to warming up an IP address.
- Consistent sending: Maintaining a consistent sending schedule after the initial warm-up period is crucial for sustaining a strong subdomain reputation.
- Monitoring deliverability: Closely monitor bounce rates, spam complaints, and ISP feedback loops. Promptly addressing these issues is paramount for successful warm-up. This is also covered in how to run an email deliverability test.
- List hygiene: Regularly cleaning your email list to remove invalid or inactive addresses is crucial, as spam traps and bounces can severely damage a new subdomain's reputation. Learn more about email best practices.
Expert view
Deliverability Expert from SpamResource confirms the importance of engagement, stating that high engagement rates, including opens, clicks, and replies, are pivotal during subdomain warm-up to signal positive sender behavior to mailbox providers.
Expert view
Deliverability Expert from WordToTheWise suggests careful list segmentation, noting that segmenting your audience to send initial warm-up volumes to highly engaged subscribers can significantly accelerate the reputation-building process.
What the documentation says
Official documentation and guides from email service providers and industry experts consistently emphasize the need for a structured warm-up process for new subdomains. While the specifics may vary, core recommendations include starting with low volume, gradually increasing sends, and meticulously configuring authentication protocols to establish trust with mailbox providers. Many highlight the similarity between domain and IP warm-up methodologies.
Key findings
- Warm-up similarity: Domain warm-up procedures, including for subdomains, closely resemble manual IP warm-up, requiring controlled increases in daily sending volume.
- Definition of domain warming: It is defined as the methodical process of incrementally increasing the email volume sent from a new domain to enhance its overall reputation.
- Structured schedules: Recommended schedules often suggest starting with a very low volume for a few days, then doubling the volume gradually over subsequent days.
- Authentication necessity: Proper configuration of email authentication protocols (SPF, DKIM, DMARC) for new subdomains is a foundational step for deliverability.
Key considerations
- Configuration checks: Documentation often advises ensuring that domains or subdomains are properly configured before slowly integrating them into the sending flow.
- Audience segmentation: Segmenting your audience can help manage the gradual increase in email volume more effectively during the warm-up period. This is crucial for warming a new email sender address.
- Four-step process: Setting up an email with a subdomain typically involves four steps: naming the subdomain, configuring authentication, warming it up, and then sending. For more, see our guide to authentication.
- Dedicated subdomain use: Best practices suggest using a unique subdomain for email sending, separate from other website or service uses, to protect its reputation. You can also review the basics of email subdomains.
Technical article
Documentation from Mailgun states warm-up similarity, explaining that domain warm-up procedures closely resemble manual IP warm-up, requiring a controlled daily increase in sending volume to build reputation effectively.
Technical article
Documentation from SendLayer defines domain warming as the methodical process of incrementally increasing the email volume sent from a new domain. This process is undertaken to enhance its overall reputation with mailbox providers.
Related resources
5 resources
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