What domain should I use for a PTR record for shared IPs?
Michael Ko
Co-founder & CEO, Suped
Published 26 Jun 2025
Updated 17 Aug 2025
9 min read
When managing email infrastructure, especially for a sending platform or a large organization, establishing the correct Pointer (PTR) records for your IP addresses is crucial. PTR records are fundamental to reverse DNS, allowing an IP address to resolve back to a hostname. This reverse lookup is a key factor in email deliverability, as it helps mailbox providers verify the sender's legitimacy.
The process becomes more nuanced when you are using shared IP addresses. Unlike dedicated IPs, where a PTR record often points directly to a client's specific sending domain, shared IPs serve multiple domains. This means a single PTR record must represent the collective identity of all senders utilizing that IP.
The choice of domain for a shared IP's PTR record significantly impacts sender reputation and inbox placement. A poorly configured or generic PTR record can trigger spam filters, leading to emails being flagged or even outright rejected. Getting this right is vital for maintaining a strong sending reputation and ensuring your emails reach their intended recipients.
Understanding PTR records and reverse DNS
A PTR record, also known as a Pointer record, facilitates reverse DNS lookup. While an A record translates a domain name into an IP address, a PTR record performs the opposite function, mapping an IP address back to its associated hostname or domain name. This reverse mapping is essential for email authentication, providing an additional layer of verification that the sending IP address is legitimately linked to the domain claiming to send the email.
For email, the PTR record primarily serves to build trust. When a mail server receives an email, it often performs a reverse DNS lookup on the sending IP address. If the IP's PTR record resolves to a legitimate hostname, it signals that the sender is identifiable and likely not a spammer. A missing or misconfigured PTR record can raise red flags, contributing to a lower sender score and increasing the likelihood of messages landing in the spam folder.
It's important to understand that the entity that owns the IP address is responsible for setting its PTR record. If you are using an Email Service Provider (ESP) or cloud hosting, they typically manage these records for you. You can learn more about how PTR records work and how they're used. For best practices related to these records and domain alignment, consult our guide on PTR records and domain alignment.
The challenge of shared IP addresses
Shared IP addresses are used by multiple senders, often by ESPs, to send emails on behalf of various clients. While cost-effective and convenient, they present a unique challenge for PTR record configuration. Unlike a dedicated IP that can have its PTR record set to reflect a single client's sending domain, a shared IP must account for all domains that use it.
Because only one PTR record can exist per IP address, it cannot point to every single client's domain. Attempting to do so would lead to conflicts and invalid configurations. This limitation means the PTR record for a shared IP must point to a neutral hostname that represents the ESP or the service provider itself, rather than any individual client.
This situation highlights a fundamental difference between shared and dedicated IP addresses. On a shared IP, while the individual sending domains (from addresses) will likely align with SPF and DKIM, the PTR record will not align with those specific domains. This is generally accepted by mailbox providers, provided the PTR record is properly configured to identify the actual sending infrastructure.
Choosing the right domain for shared IP PTR records
For shared IP addresses, the PTR record should resolve to a hostname that clearly identifies the organization operating the mail server, typically the Email Service Provider (ESP). This hostname should convey that the server is intended for sending email and is part of a legitimate infrastructure. For instance, if your ESP's domain is exampleesp.com, a suitable PTR record might be mail.exampleesp.com or mta.exampleesp.com. Using subdomains like mail1.pool.exampleesp.com can also indicate a pool of mail servers.
The key is consistency and clarity. Maintain a consistent naming scheme across all your shared IPs. This practice helps mailbox providers easily identify your sending infrastructure and build a positive reputation over time. Avoid generic or auto-generated hostnames that do not clearly represent your organization or appear dynamic. Such names can be mistaken for spamming attempts or compromised servers.
While some might use parts of the IP address in the PTR hostname (e.g., mta-xx-yy.domain.com), this approach can be problematic with certain mailbox providers. Some, like T-Online, may interpret numeric patterns in PTR records as indicators of dynamic or less reputable sending sources, impacting your deliverability. Focus on a clear, static, and brand-aligned hostname.
Good PTR record examples
ESP-specific:mail.your-esp-domain.com
Mail server identification:mta1.your-esp-domain.com
Pool identification:pool.your-esp-domain.com
For a comprehensive understanding, explore how reverse DNS should be configured for both shared and dedicated IPs, and how to spot problematic ESP configurations. Understanding these nuances is crucial for maintaining optimal email deliverability.
Impact on email deliverability
The PTR record plays a significant role in how mailbox providers assess the trustworthiness of incoming email. When the PTR record aligns with the sending IP's legitimate purpose (e.g., a mail server for an ESP), it contributes positively to your sender reputation. Conversely, a mismatch or a generic PTR record can harm your reputation.
Mailbox providers, including Gmail and Yahoo, extensively use PTR lookups as part of their spam filtering algorithms. They expect the PTR record to resolve to a hostname that indicates a valid sending server. If an IP address on a shared pool has a suspicious PTR, it could lead to blocklisting (or blacklisting) for that IP, affecting all senders who use it. You can review how PTR records are used for emailing to further understand their significance.
Regular monitoring of your IP's reputation, including its PTR record status, is essential. Tools for checking blocklists can help identify issues quickly. A well-maintained PTR record for shared IPs ensures that the foundational layer of your email authentication is strong, contributing to higher inbox placement rates for all users of that IP. It is also important to check if the sending IP matches the PTR hostname.
Maintaining deliverability with shared IPs
Even though a shared IP has a single PTR record, you can still implement DMARC with shared IP addresses. DMARC alignment primarily relies on SPF and DKIM authentication, which are typically configured at the sending domain level, not necessarily directly tied to the PTR record. However, a strong PTR record contributes to the overall trust signals that DMARC-checking servers consider.
For platforms sending on behalf of multiple clients, a key consideration is whether shared rDNS becomes an issue. Generally, if the PTR record identifies the ESP clearly and consistently, it's not a major issue, as mailbox providers understand this operational model. The focus remains on strong SPF and DKIM authentication for individual client domains.
Remember, the overarching goal is to present a cohesive and trustworthy sending identity. While a shared IP's PTR record won't directly align with individual client domains, its proper configuration is part of the broader strategy for establishing and maintaining good email deliverability across the shared infrastructure.
Views from the trenches
Best practices
Always use a consistent and recognizable hostname for your PTR records that clearly identifies your organization or mail server.
Ensure the PTR record resolves to a domain you own and control, preferably a subdomain specifically for mail services.
Choose a hostname that indicates it is a mail server, such as 'mail.yourdomain.com' or 'mta.yourdomain.com'.
Verify that your PTR record matches the hostname your sending server announces during the SMTP handshake.
Common pitfalls
Using generic or dynamic-looking hostnames in PTR records, such as those with random words or full IP addresses.
Having a missing PTR record, which severely impacts deliverability and reputation.
Allowing the PTR record to point to a client's specific domain on a shared IP, leading to misalignments.
Ignoring mailbox provider specific preferences, such as T-Online's dislike for numeric patterns in PTR records.
Expert tips
Keep the PTR record simple and descriptive; it is primarily for machine and human identification.
Regularly monitor your IPs on blocklists (blacklists) to ensure your PTR record isn't causing issues.
Understand that even with shared IPs, strong SPF and DKIM alignment are critical for DMARC pass.
Communicate PTR record configuration clearly to clients using shared IPs to manage expectations.
Expert view
Expert from Email Geeks says the hostname chosen for a shared IP's PTR record should clearly indicate ownership and that it is a mailserver, recommending consistent naming schemes like mail13.esp.com or mail13.pool.esp.com.
2024-07-04 - Email Geeks
Expert view
Expert from Email Geeks says avoiding random word hostnames like banana-hotdog.esp.com is crucial, as they can appear as snowshoe spam.
2024-07-04 - Email Geeks
Key takeaways for shared IP PTR records
For shared IP addresses, the ideal domain for your PTR record is a sub-domain of your Email Service Provider's (ESP) main domain. This hostname should clearly signify its role as a mail server and maintain a consistent, identifiable naming convention. It should be generic enough not to represent any single client, yet specific enough to belong unmistakably to your sending infrastructure. This approach ensures that your PTR record contributes positively to your overall sender reputation and email deliverability.
By adhering to these guidelines, you can navigate the complexities of shared IP PTR records effectively, minimizing the risk of deliverability issues and ensuring your emails reliably reach the inbox. Remember that a strong PTR record, alongside robust SPF and DKIM implementation, forms the cornerstone of a healthy sending reputation.
Gmail and 
Yahoo, extensively use PTR lookups as part of their spam filtering algorithms. They expect the PTR record to resolve to a hostname that indicates a valid sending server. If an IP address on a shared pool has a suspicious PTR, it could lead to blocklisting (or blacklisting) for that IP, affecting all senders who use it. You can review how PTR records are used for emailing to further understand their significance.
