How can I check if an email is sent from a dedicated or shared IP without contacting the ESP?

Key findings

• Email headers: The Received header reveals the sending IP address. Analyzing this is the first step.
• Reverse DNS (PTR record): Checking the reverse DNS (PTR) record of the sending IP can offer clues. A customer-specific PTR record often points to a dedicated IP, while a generic or ESP-branded PTR might indicate a shared pool. Learn more about reverse DNS resolution best practices.
• IP reputation services: Tools like SenderScore can show how many domains are associated with a particular IP. A high number of associated domains typically suggests a shared IP.
• SPF record: If the sender's SPF record directly includes the sending IP, it's likely dedicated. If it only includes the ESP's record, it could be either shared or dedicated. Understand the full form of SPF.

Key considerations

• No definitive external method: Many ESPs structure their IP ranges in a way that makes it intentionally difficult to distinguish shared from dedicated IPs from the outside.
• Return-path unreliability: The return-path domain belonging to the ESP does not automatically indicate a shared IP, as some ESPs offer clients the option to white label their return-path.
• Dynamic IP allocation: Some cloud-based ESPs (e.g., those using AWS SES) might issue dynamic or elastic IPs, making consistent identification challenging.

Key opinions

• Header analysis: Many marketers begin by manually analyzing email headers, looking for differences in configuration between emails from known dedicated IPs and unknown sources. This helps them determine the sending platform.
• Sender score and associated domains: Using tools that report an IP's sender score and the domains associated with it is a common tactic. If an IP shows many domains sending through it, it's often inferred to be shared.
• Seedlist testing: For senders who can control the mail stream (e.g., their own ESP), sending to a seedlist and observing whether messages arrive from multiple IPs (shared) or consistently from one IP (dedicated) can be revealing.
• Pattern recognition: Marketers often rely on spotting patterns across multiple emails from the same sender or ESP to make educated guesses, especially for dedicated IPs they already know.

Key considerations

• Initial assumptions can be flawed: For example, assuming a return-path domain belonging to the ESP means a shared IP is not always correct, due to white-labeling options.
• Manual analysis limitations: While manual analysis can provide hints, it's not scalable or definitively accurate for automated detection. This can affect email deliverability issues.
• Limited external view: Without being able to send emails through a platform, it's harder to use techniques like seedlist testing to identify IP types from the outside.
• Sender reputation awareness: Marketers often check email sending reputation using various tools, which can implicitly suggest shared versus dedicated status based on the diversity of associated domains.

Key opinions

• Reverse DNS as an indicator: Experts suggest that examining the reverse DNS (PTR record) of the IP address found in the email headers is a key step. A customer-specific rDNS indicates a dedicated IP, while a generic or ESP-named rDNS might signify a shared pool.
• SPF record insights: If the sender's SPF record explicitly lists the sending IP, it points to a dedicated setup. If it merely includes the ESP's broader record, it's less conclusive.
• Seedlist tool reports: Deliverability experts use seedlist tools, which provide reports detailing all IPs and their PTR records from which messages arrived, making it easier to spot shared pools (multiple IPs) versus dedicated (single IP).
• No definitive external solution: A strong consensus among experts is that there's no single, definitive way to ascertain an IP's status without asking the ESP directly. This highlights the inherent difficulty in maintaining dedicated IP reputation.

Key considerations

• ESPs obscure details: Many ESPs utilize IP ranges where both shared and dedicated IPs appear identical externally, making differentiation challenging.
• Automation challenges: While manual hints exist, automating accurate detection of shared versus dedicated IPs is a hard problem due to varying configurations and dynamic IP allocations (e.g., elastic IPs from services like Amazon SES).
• Changing IP ranges: Some large ESPs, like Klaviyo, explicitly state that their IP ranges can change, further complicating static identification efforts. This affects how ESPs manage IP pools.
• SenderScore API limitations: While SenderScore provides valuable information, there is no free and public API to programmatically access the comprehensive list of domains associated with an IP, which limits automated detection.
• Shared IP deliverability: Experts note that shared IPs can offer flexibility, especially for senders with low or inconsistent volumes, as discussed in Kickbox's expert advice.

Key findings

• Dedicated IP definition: Documentation defines a dedicated IP as a unique, static IP address used exclusively by a single sender, offering full control over their sending reputation.
• Shared IP definition: A shared IP, conversely, is one utilized by multiple senders, where the collective sending behavior of all users on the IP impacts its reputation.
• Reputation implications: The type of IP (dedicated or shared) directly influences an organization's sender reputation and, consequently, its email deliverability.

Key considerations

• Choosing the right IP type: Documentation from platforms like Mailgun often details the scenarios when a dedicated IP is necessary versus when a shared IP is sufficient, based on sending volume and consistency. For further insights, refer to when to use a shared IP.
• ESP role: ESPs are responsible for managing IP pools and assigning IPs. Their internal infrastructure setup heavily influences how IPs are used and if their nature can be externally discerned. This ties into how ESPs impact deliverability.