Can a subdomain inherit the reputation of its main domain?

A subdomain can benefit from the general trust associated with its parent domain, especially in terms of age. However, its own sending practices, combined with the reputation of the IP addresses it uses, will establish its unique sender reputation over time.

How long does it take to warm up a new IP address for an existing subdomain?

The warming period varies depending on your sending volume and the target mailbox providers. It can range from a few weeks to several months. The key is to gradually increase volume and monitor performance closely.

Should I use different subdomains for transactional and marketing emails?

Yes, it is highly recommended to use separate subdomains and ideally separate IP addresses for different email types. This isolates the reputation of each stream, protecting your critical transactional emails from potential issues with marketing campaigns. More on this here: should I use subdomains for transactional and promotional emails .

What are the risks of using the same subdomain with two different IPs without proper setup?

Without proper SPF, DKIM, and DMARC configuration across both IPs, emails may fail authentication, leading to higher spam folder placement or rejections. It can also confuse mailbox providers, negatively impacting the subdomain's overall reputation and potentially leading to blocklist (or blacklist) listings for your IPs.

How do Google and Yahoo treat subdomains with multiple IPs?

Google and Yahoo assess both IP and domain (subdomain) reputation. They look for consistent, authenticated sending patterns. While they might aggregate reputation signals across related subdomains, each IP's performance contributes significantly to the specific subdomain's standing. They emphasize proper authentication and adherence to their sender guidelines. You can check Google's guidelines here .

How to manage subdomain reputation when using multiple IP addresses for email sending? - Sender reputation - Email deliverability - Knowledge base

When you're handling email sending for a growing business, you might find yourself needing to use multiple IP addresses, perhaps for different email types or even when transitioning between email service providers. A common challenge arises when you also want to maintain or leverage the existing reputation of your subdomains. It's a tricky balance to strike, as poor management can significantly impact your inbox placement.

The good news is that it's entirely possible to navigate this complexity successfully. The key lies in understanding how IP and domain reputation interact and implementing precise technical configurations and consistent sending practices. I'll share insights into how to keep your email streams healthy and ensure your messages reach their intended recipients, even with multiple IPs in play.

Understanding reputation with multiple IP addresses and subdomains

When you send emails, both your IP address and your domain (including subdomains) build a reputation with mailbox providers. While IP reputation is tied to the specific server sending the email, domain reputation is portable and follows your domain, regardless of the underlying IP. This distinction is crucial when you introduce multiple IP addresses for the same subdomain or related subdomains. It's important to understand how domain reputation works with subdomains.

Mailbox providers, like Google and Yahoo, look at both IP and domain reputation to determine whether to deliver your emails to the inbox, spam folder, or reject them entirely. If you're using multiple IP addresses for a subdomain, the reputation of each IP address will contribute to the overall perception of that subdomain. A sudden change in IP or sending behavior can trigger flags, even if your domain reputation is strong. You can learn more about IP and domain reputation here.

Using subdomains strategically is a common practice to segment email traffic, such as separating transactional emails from marketing campaigns. This segmentation helps isolate the reputation of different email streams. For instance, if your marketing emails encounter issues that lead to a blocklist (or blacklist) listing, your transactional emails sent from a different subdomain and IP might remain unaffected. This is why many senders choose to use subdomains for email marketing deliverability.

Keeping existing subdomains with new IPs

When migrating to a new email service provider or adding a new sending platform, you might want to retain your existing subdomains due to their established reputation. This approach involves careful configuration and warming.

Authentication alignment: Ensure SPF, DKIM, and DMARC are properly configured for both the legacy and new IP addresses. SPF records for each sending provider should be distinct.
Gradual warming: Even with an established subdomain, the new IP address needs a proper warm-up period. Start with low volumes and gradually increase, allowing mailbox providers to build trust in the new IP's sending patterns. You will need to warm up a subdomain.
DNS management: Manage DNS records carefully, especially for things like click tracking domains. You might need to set up new, unique hostname DNS entries under a new subdomain on the new platform, then map your existing From: address on top.

Creating new subdomains for new IPs

An alternative is to create entirely new subdomains for your new IP addresses. While this requires building reputation from scratch, it offers a cleaner separation and can simplify migration.

Reputation isolation: New subdomains ensure complete isolation of reputation. If the new sending stream encounters issues, your established subdomains remain unaffected.
Dedicated warming: Each new subdomain and its associated IP(s) will require dedicated IP warming. This process is crucial for establishing a healthy sender reputation.
Simplified DNS: Avoids potential conflicts with existing DNS records (e.g., click tracking) tied to older platforms. You can configure new, clean DNS entries for each new subdomain.
Brand consistency: While using new subdomains, maintain brand consistency in your 'From' names and email content.

Technical setup and authentication

Proper email authentication is non-negotiable when managing multiple IP addresses and subdomains. This includes SPF, DKIM, and DMARC. SPF records define which IP addresses are authorized to send on behalf of your domain. With multiple IPs, your SPF record will need to include all authorized sending sources. Remember, you might need different SPF domains for each sending setup, but you can use the same d= domain with different selectors for each sending setup.

DKIM (DomainKeys Identified Mail) adds a digital signature to your emails, verifying that the email has not been tampered with and truly comes from your domain. Each sending platform might require its own DKIM key and selector, even for the same subdomain. Ensuring proper DKIM alignment is essential for successful email delivery. This aligns with a simple guide to DMARC, SPF, and DKIM.

DMARC (Domain-based Message Authentication, Reporting, & Conformance) builds on SPF and DKIM, allowing you to tell mailbox providers how to handle emails that fail authentication and provides valuable reports. Implementing a DMARC policy with a p=none initially is a good practice, allowing you to monitor results before moving to stricter policies like quarantine or reject. These reports are invaluable for understanding how your different IP addresses and subdomains are performing.

Reverse DNS (rDNS) is another critical, yet often overlooked, component. It ensures that your sending IP address resolves back to your sending domain. While you might have multiple IP addresses, each should have a correctly configured rDNS entry that matches the subdomain from which it sends. Incorrect rDNS can lead to emails being flagged as spam. For more on this, consult how to configure rDNS.

DNS records for marketing.example.com on two different IP addressesDNS

marketing.example.com. IN A 192.0.2.1
marketing.example.com. IN A 198.51.100.2

marketing._domainkey.example.com. IN TXT "v=DKIM1; k=rsa; p=MIGfMA0GCSqGSIb3DQEBAQUAA4GNADCBiQKBgQD7hG..." (for IP 192.0.2.1)
marketing2._domainkey.example.com. IN TXT "v=DKIM1; k=rsa; p=MIGfMA0GCSqGSIb3DQEBAQUAA4GNADCBiQKBgQD8jS..." (for IP 198.51.100.2)

_dmarc.example.com. IN TXT "v=DMARC1; p=none; fo=1; ruf=mailto:reports@example.com; rua=mailto:aggreports@example.com"

Managing IP and subdomain warming

Even when using an existing subdomain with a strong reputation, introducing new IP addresses means you must warm them up. IP warming is the process of gradually increasing the volume of email sent from a new IP address over a period. This allows mailbox providers to recognize the IP as a legitimate sender and build a positive sending history. Failing to warm up can lead to immediate blocklisting or heavy throttling. You can learn how to warm up a subdomain and its associated IP addresses.

The warming schedule depends on your sending volume and the recipient mailbox providers. Start with small volumes to highly engaged subscribers and slowly scale up. Monitor your reputation metrics closely, such as bounce rates, spam complaint rates, and open rates. If you see signs of trouble, reduce volume and investigate. This process is crucial to maintaining dedicated IP reputation with ISPs.

It's important to understand that some mailbox providers also look across multiple subdomains to calculate your reputation. This means that while isolating traffic helps, a severe reputation hit on one subdomain might still have a minor ripple effect. Consistent sending practices across all subdomains and IPs are vital for holistic deliverability. You can refer to this resource for more on subdomain segmentation and filtering technologies.

During periods of transition or dual sending, it’s advisable to segment your audience and send lower volumes through the new IP, reserving higher volumes for the established IP, if possible. This phased approach minimizes risk. Monitor your campaign performance on both IPs and adjust your sending strategy as the new IP gains trust.

Key considerations for dual sending

When a subdomain is accessed through two different IP addresses (e.g., during a platform migration), consider the following:

Inbound mail: A subdomain can only truly receive inbound mail at one destination. If your subdomains are used for reply-to addresses, you need to ensure inbound mail is directed to a single platform.
Click tracking: Each sending platform (new and old) might require unique hostname DNS entries for features like click tracking. You cannot use the same click tracking domain for two platforms simultaneously. You may need to set up a new tracking domain (e.g., track.newtool.example.com) alongside your primary sending subdomain. This is highlighted in email deliverability overview for DNS setup.
Unified reporting: Consolidate reports from both sending platforms to get a holistic view of your deliverability and engagement metrics for the subdomain.

Ongoing monitoring and best practices

Managing subdomain reputation with multiple IPs is an ongoing process that requires diligent monitoring. Regular checks of your sender reputation metrics are essential. Utilize tools like

Google Postmaster Tools for Gmail data or similar tools for

Outlook to gain insights into your sending performance, spam rate, and IP/domain reputation. This helps you identify and address issues promptly. For a deeper dive, review their insights on how to improve domain reputation.

Proactive

blocklist monitoring (or blacklist monitoring) is also critical. If any of your IP addresses or subdomains appear on a blocklist, it can severely impact your deliverability. Prompt action, including delisting requests and identifying the root cause of the listing, is necessary. Having a process for monitoring blocklists is vital.

Beyond technical configuration and monitoring, adherence to email sending best practices is paramount. This includes sending wanted email, maintaining a clean and engaged subscriber list, processing opt-outs promptly, and avoiding sending to invalid or role-based addresses. High engagement rates and low complaint rates across all your sending IPs and subdomains will naturally build and sustain positive reputation. For more details, consider the guide to managing email reputation.

Views from the trenches

Best practices

Warm up new IP addresses thoroughly, even if using an established subdomain, to build trust with mailbox providers.

Ensure all email authentication protocols (SPF, DKIM, DMARC) are correctly configured for every sending IP and subdomain.

Regularly monitor your sending metrics and blocklist status for all IP addresses and subdomains.

Common pitfalls

Assuming a new IP address will inherit the full reputation of an existing subdomain without proper warming.

Not configuring unique DNS entries for features like click tracking across different sending platforms.

Overlooking the impact of inbound mail routing when managing subdomains on multiple platforms.

Expert tips

Use different DKIM selectors for each sending setup while maintaining the same DMARC domain for consistency.

Implement a phased transition when moving platforms, gradually shifting sending volume to new IPs.

Consolidate reporting from all sending platforms to gain a complete picture of your email program's health.

Expert view

Expert from Email Geeks says that if you are using subdomains for email addresses in the From: header, you can do aligned authentication with SPF and DKIM from both providers simultaneously, but you will still want to ramp up the volume gradually from the new provider for it to be fine.

November 13, 2023 - Email Geeks

Marketer view

Marketer from Email Geeks says that you need to make sure your SPF domains are different from each other, but you can use the same d= domain with different selectors for each sending setup.

December 1, 2023 - Email Geeks

Ensuring robust deliverability with multiple IP addresses

Managing subdomain reputation when using multiple IP addresses for email sending is a complex but manageable task. The core principles revolve around strategic subdomain use, meticulous technical configuration of authentication protocols (SPF, DKIM, DMARC), careful IP warming, and continuous monitoring. By adhering to these practices, you can segment your email traffic, protect your sender reputation, and optimize your email deliverability.

While the technical nuances can be challenging, the effort invested in proper setup and ongoing vigilance pays significant dividends in inbox placement and overall email program success. Remember that consistency in your sending behavior and a focus on recipient engagement will always be the bedrock of a strong email reputation, regardless of how many IP addresses or subdomains you employ.