Can I use multiple subdomains with one dedicated IP?

You can absolutely use multiple subdomains with a single dedicated IP address. The primary reason for doing this is to segment your email streams and manage their reputations independently. For example, you might have one subdomain for transactional emails and another for marketing emails, both sending from the same IP. This isolates any potential deliverability issues of one stream from affecting the other.

What is the recommended email volume for a single dedicated IP?

For a single dedicated IP, a general guideline is to send at least 100,000 to 200,000 emails per month to establish and maintain a good sending reputation. If your volume is significantly lower or inconsistent, a shared IP might be more suitable. However, if you're sending high-volume, consistent email (e.g., up to 1.5 million monthly ), one dedicated IP can suffice, especially with proper subdomain segmentation.

How does the PTR record affect using multiple subdomains on one IP?

The PTR (Pointer) record, also known as a reverse DNS record, creates a one-to-one mapping between an IP address and a hostname. While you can send emails from multiple subdomains through a single dedicated IP, the PTR record for that IP can only resolve to a single canonical hostname. Typically, you'd choose the subdomain responsible for your highest volume or most reputation-sensitive email stream as the canonical hostname for the PTR record.

What happens if one of my subdomains gets a bad reputation while sharing an IP?

If you experience deliverability issues on one subdomain, such as being placed on a blocklist or seeing emails go to spam, the reputation damage is largely contained to that specific subdomain. Your other subdomains, even if they share the same dedicated IP, are less likely to be affected directly, especially for mailbox providers that rely heavily on domain-level reputation. This allows you to address the issue on the problematic subdomain without disrupting your entire email program.

Is IP warming necessary when moving to a dedicated IP with existing subdomains?

Yes, it is crucial to warm up your dedicated IP address when you first start using it, even if you are moving from another dedicated IP. IP warming involves gradually increasing your email sending volume over several weeks to build a positive reputation with mailbox providers. Failing to warm up your IP can lead to poor deliverability, emails being rejected, or your IP being placed on a blacklist or blocklist from the start.

How many subdomains should I use per dedicated IP address for email sending? - Sender reputation - Email deliverability - Knowledge base

Moving to a dedicated IP address for email sending is a significant step for businesses looking to enhance their email deliverability. A common question that arises during this transition is how many subdomains should be used per dedicated IP address.

The relationship between subdomains and dedicated IPs isn't always a simple one-to-one mapping. It often depends on your email sending strategy, the types of emails you send, and your desired level of sender reputation management.

This decision significantly impacts how your emails perform, influencing factors like inbox placement and your ability to recover from deliverability issues. Let's explore the factors to consider when determining the optimal number of subdomains for your dedicated IP setup.

Understanding the role of subdomains

Subdomains play a crucial role in segmenting your email traffic and managing your sender reputation. Instead of sending all email types from your main domain, using subdomains allows you to isolate different mail streams.

For instance, you might use marketing.yourdomain.com for promotional newsletters and transactional.yourdomain.com for order confirmations or password resets. This segmentation is vital because the reputation of one subdomain doesn't directly impact others.

Should your marketing emails encounter deliverability issues, perhaps due to lower engagement or complaints, the reputation of your transactional subdomain remains unaffected, ensuring critical communications continue to reach the inbox. This strategy is a fundamental part of a robust email deliverability framework, allowing for better control over how your emails are perceived by mailbox providers.

Why use separate subdomains?

Using separate subdomains for different email types helps isolate reputation. If one stream, like marketing, experiences issues, it prevents collateral damage to your critical transactional emails. This approach enhances your overall domain reputation.

DNS configuration

Each subdomain requires its own DNS records for authentication, including SPF, DKIM, and DMARC. This ensures that each sending stream is properly authenticated and trusted by mailbox providers, improving the chances of reaching the inbox rather than the spam folder.

Dedicated IP addresses and sending volume

A dedicated IP address is an exclusive IP used solely by your organization for email sending. Unlike shared IPs, where your sender reputation is influenced by other users, a dedicated IP gives you complete control over your sending reputation. This control is a double-edged sword, as your practices directly dictate your deliverability.

Generally, a dedicated IP is recommended for senders with consistent, high email volumes. Many providers suggest a minimum of 100,000 to 200,000 emails per month to adequately warm up the IP and maintain a healthy reputation.

If your volume is too low or inconsistent, a dedicated IP can struggle to build a positive sending history, potentially leading to worse deliverability than a shared IP. Conversely, high-volume senders benefit immensely from the direct control and consistent reputation building that a dedicated IP offers, minimizing the risk of being blocklisted or blacklisted due to others' poor sending practices.

Monthly Email Volume	Recommended IP Addresses	Considerations
Under 100,000	Shared IP (or 1 dedicated if consistently growing)	May struggle to warm a dedicated IP.
100,000 - 500,000	1 dedicated IP	Good volume for reputation building.
500,000 - 1,000,000	1-2 dedicated IPs	Consider adding a second IP for high volume or segmentation.
Over 1,000,000	Multiple dedicated IPs	Essential for distributing volume and isolating streams.

One-to-one vs. many-to-one relationships

The core of your question, how many subdomains per dedicated IP, doesn't have a universal one-size-fits-all answer. It primarily hinges on your email streams. You can absolutely map multiple subdomains to a single dedicated IP address. This is a common and effective strategy.

Leading email service providers often recommend using a separate subdomain for each distinct sending purpose, even if those purposes share the same IP. For instance, news.yourdomain.com for newsletters and alerts.yourdomain.com for critical notifications could both send from the same dedicated IP.

The key here is that while multiple subdomains can be configured to send via the same IP, your PTR (Pointer) record, also known as a reverse DNS record, must resolve to a single canonical hostname. This hostname is typically one of your sending subdomains, and it should match the IP address.

Example DNS records for a dedicated IP and subdomainDNS

v=spf1 include:_spf.example.com ~all
hosts.yourdomain.com. IN A 192.0.2.1
1.2.0.192.in-addr.arpa. IN PTR hosts.yourdomain.com.

This means that while different subdomains might be used for sender reputation, only one can be used for the PTR record. The selection of this primary subdomain is usually based on the highest volume or most reputation-sensitive email stream.

One subdomain per dedicated IP

Simplicity: Easier to manage DNS records and authentication (SPF, DKIM, DMARC).
Clear reputation: Reputation is directly tied to a single email stream and IP.
Ideal for: Organizations with a single, high-volume email type or very distinct email purposes requiring separate IPs.

Multiple subdomains per dedicated IP

Reputation segmentation: Isolates the reputation of different email streams (e.g., transactional, marketing, alerts) while sharing the same IP.
Resource efficiency: Maximizes use of a single dedicated IP's capacity.
Ideal for: Organizations with diverse email types but not enough volume to justify multiple dedicated IPs, or where reputation isolation is paramount.

Factors influencing your decision

When deciding on your subdomain and dedicated IP strategy, several factors should guide your approach. The most critical is the purpose and nature of your email sending.

For example, highly critical transactional emails like password resets or two-factor authentication codes should always be segregated from bulk marketing or promotional sends. Even if they share the same dedicated IP, giving them a distinct subdomain protects their sender reputation, making them less susceptible to issues arising from marketing campaigns. This is where multiple subdomains per IP shines.

Your sending volume and consistency also play a role. If your daily or monthly sending volume is significant but not high enough to warrant multiple dedicated IPs (e.g., 50,000 emails per day, as some suggest can be handled by a single IP, or even up to 1 million emails daily with good reputation), then leveraging multiple subdomains on that single IP is an effective way to manage reputation by stream. This ensures that a sudden spike in complaints for promotional emails doesn't jeopardize the deliverability of your critical transactional emails.

Ultimately, the optimal setup is a balance between technical feasibility and strategic reputation management. It's about ensuring your most important emails always land in the inbox, while allowing for more flexible, and potentially riskier, sending practices for other types of communications. Continuously monitoring your blocklist status and engagement rates across your subdomains will provide valuable insights into whether your current strategy is effective or if adjustments are needed.

Views from the trenches

Best practices

Maintain a consistent sending volume for each email stream to build and maintain a strong reputation for your dedicated IP.

Segment your email types, like transactional and marketing, into distinct subdomains to isolate their sender reputations.

Implement robust email authentication protocols, including SPF, DKIM, and DMARC, for all your sending subdomains.

Regularly monitor your email deliverability metrics for each subdomain to identify and address issues proactively.

Warm up your dedicated IP gradually when migrating, starting with small volumes and slowly increasing them over time.

Common pitfalls

Using a single subdomain for all email types can put your entire email program at risk if one stream encounters deliverability issues.

Not maintaining consistent sending volume on a dedicated IP can lead to its reputation decaying, impacting deliverability.

Failing to set up proper authentication for all subdomains can result in emails being flagged as spam or rejected by mailbox providers.

Ignoring feedback loops and recipient complaints can quickly degrade your dedicated IP's reputation.

Moving too quickly to full volume on a new dedicated IP without proper warming can lead to immediate blacklisting or poor inbox placement.

Expert tips

Align your subdomain strategy with the specific reputation requirements of each mail stream, not just the volume.

Prioritize the reputation of transactional subdomains, as their deliverability is critical for user experience and business operations.

Leverage DMARC reporting to gain visibility into authentication failures and potential reputation issues across your subdomains.

If you introduce new types of content or significantly change sending patterns, adjust your subdomain strategy to mitigate risk.

Consider the long-term growth of your email program when planning your IP and subdomain infrastructure.

Expert view

Expert from Email Geeks says the number of subdomains per dedicated IP depends entirely on the types of emails being sent.

2024-02-16 - Email Geeks

Marketer view

Marketer from Email Geeks says that a separate subdomain should be used for each distinct mail stream. If only one type of email is sent, then only one subdomain is needed, regardless of how many IPs are used.

2024-02-16 - Email Geeks

Strategic subdomain and IP allocation

The ideal number of subdomains per dedicated IP address for email sending isn't a fixed rule, but rather a strategic decision based on the complexity and volume of your email streams. While a single dedicated IP can support multiple subdomains, the key is to align your subdomain strategy with the specific needs of each email type.

Prioritizing the segregation of sensitive transactional emails from bulk promotional sends, regardless of shared IP, is paramount for maintaining high deliverability. This approach helps to protect your core email communications from potential reputation damage.

By carefully considering your email volume, the consistency of your sends, and the various purposes of your email campaigns, you can create a setup that optimizes sender reputation, ensures reliable inbox placement, and supports the long-term success of your email program.