Summary
Email Service Providers (ESPs) often employ sophisticated strategies to manage sender reputation, particularly concerning shared IP pools and the use of their own sending domains versus client domains. The core challenge lies in balancing the benefits of shared resources with the potential risks posed by a single bad actor's impact on collective reputation. While IP segregation helps in granular management, the interplay with domain reputation, especially when ESPs use common domains for various clients, introduces complexities. Understanding this dynamic is crucial for both ESPs and their clients to maintain optimal email deliverability.
Key findings
- Reputation components: Sender reputation is a multifaceted construct, primarily influenced by the DKIM signing domain, the sending IPs, and the 5322.FROM domain. The 5321.MAILFROM domain (return-path) is typically used by the ESP for bounce management and generally doesn't factor into individual sender reputation unless the ESP is considered 'spammer friendly'.
- IP segregation benefits: ESPs segmenting customers by IP (e.g., good vs. bad senders) allows mailbox providers to assess mail more granularly, mitigating the risk of poor senders impacting an entire shared pool.
- Domain reputation risk: Even with IP segregation, if ESPs do not adequately police their customers, shared ESP-owned domains (for 5321.MAILFROM, click tracking, or image hosting) can suffer from negative actions of bad senders, affecting the ESP's overall standing and potentially all its clients. Learn more about how domain reputation affects deliverability.
- Shared IP challenges: A shared IP's reputation is only as strong as its weakest sender. However, a good sender can often maintain deliverability on a poorly reputed shared IP due to other contributing factors like domain reputation.
- Tracking domain impact: Tracking domains (used for clicks, opens) are reputation data points. It is best practice for senders to use their own branded tracking domains rather than relying on an ESP's shared tracking domains, as shared domains are beyond the sender's control. See this guide to email sender reputation for more.
Key considerations
- ESP policing: The long-term health of an ESP's domain reputation depends heavily on their ability to rigorously police customer sending practices. Failure to do so can lead to a damaged domain, even if IPs are segregated.
- Delegating tracking: ESPs should offer customers the ability to use their own domains for tracking links (e.g., click.example.com), giving senders more control over their entire message footprint and reputation. This is part of a broader discussion on how email sending practices impact domain reputation.
- Dedicated IP vs. Shared IP: While moving to a dedicated IP after establishing reputation is often recommended, the effectiveness is tied to how well the sender manages their own practices, as domain reputation remains critical.
- Dual DKIM signing: For ESPs, signing emails with their own domain for DKIM (in addition to client domains if applicable) is important for various reasons, including FBLs. Senders should ideally sign with their From address domain.
What email marketers say
Email marketers often navigate the complexities of shared IP pools and domain usage with a mix of practical experience and ongoing questions. Their discussions highlight the tangible effects of these configurations on daily deliverability and the perceived risks to their sender reputation. They are keen to understand the best practices for leveraging ESP services while safeguarding their brand's email standing.
Key opinions
- Shared IP risk perception: There's a general understanding that shared IPs carry the risk of reputation being negatively affected by other senders in the same pool, regardless of their own sending practices. This can lead to IP blocklisting.
- Domain vs. IP reputation focus: Marketers frequently question whether the ESP's domain is impacted when clients use their own dedicated domains on shared IPs, indicating a strong awareness of both IP and domain reputation. This also touches on what a shared IP address means.
- Importance of dedicated domains: Many marketers are advised to transition to a dedicated domain once their sending reputation is established, suggesting a belief in greater control and protection over their reputation.
- Tracking link domain confusion: There's a query regarding whether tracking link domains impact sender reputation and if it's advisable to use the same domain for tracking as the 5321.FROM (Mail From) domain.
- ESP role in domain reputation: Marketers recognize that even if clients use their own sending domains, the ESP's infrastructure and overarching domain reputation can still be a factor, especially if the ESP allows problematic sending practices.
Key considerations
- ESP diligence: Marketers should assess an ESP's commitment to deliverability best practices and its policing of bad actors to protect their own domain reputation, even on shared IPs. This is crucial for avoiding being on an email blocklist.
- Branding tracking links: It is generally advisable to use a dedicated domain for tracking links (e.g., click.yourbrand.com) to maintain consistency and control over your brand's full email footprint.
- Understanding reputation points: Marketers need to understand that reputation is built on multiple data points beyond just the IP address, including the DKIM signing domain and the 5322.FROM domain. This comprehensive view helps in strategic decision-making regarding shared versus dedicated resources.
- Choosing the right ESP: The fundamental decision of choosing a reputable ESP that actively manages its shared IP pools and enforces good sending practices is paramount for long-term deliverability success. You can see a general guide on why emails go to spam.
Marketer view
Email marketer from Email Geeks observed that some ESPs categorize customers into different shared IP pools based on their sending behavior, like 'good' or 'bad' senders, and provide dedicated IPs from a separate pool. The marketer questioned whether this approach creates long-term domain reputation issues for the ESP if their own domains remain consistent across these varied IP pools.
Marketer view
Email marketer from Email Geeks inquired if clients (customers) using their own dedicated domains, but still operating on an ESP's shared IP, would result in the ESP's domain being negatively impacted by that client's sending practices. This highlights a common concern about the indirect effects of client behavior on the ESP.
What the experts say
Deliverability experts provide deep insights into the intricate mechanisms of email reputation, emphasizing the multiple data points Mailbox Providers (MBPs) use to evaluate incoming mail. Their perspectives often highlight the technical nuances of how IPs, various domains, and authentication protocols interact to form a sender's trustworthiness. They stress the importance of understanding these factors to build and maintain a strong sending reputation, irrespective of whether shared or dedicated IP resources are in use.
Key opinions
- Multiple reputation data points: Sending reputation is assessed using numerous data points, primarily the DKIM signing domain, the sending IPs, and the 5322.FROM domain, not just the 5321.MAILFROM domain.
- Shared IP nuance: While shared IPs are indeed affected by the worst sender in the pool, a good sender can often achieve good deliverability on a mediocre shared IP due to the cumulative effect of other positive reputation signals, especially their own domain's reputation. This is why email warming on shared IPs is important.
- ESP domain impact: An ESP's domain reputation can be affected by bad behavior on its network, even when clients use their own dedicated domains. This occurs because ESPs often host image or click tracking domains, creating a shared reputational link.
- Complex reputation interactions: Reputation is complex, involving many identifiers. While ESP reputation can be affected by clients on dedicated domains, this impact is generally less severe than with clients on shared domains. Explore more about managing IP reputation across clients.
- Tracking domain best practice: It is best practice for reputable ESPs to allow customers to delegate tracking links to their own domains. Avoiding third-party domains in the message body, if possible, is recommended due to lack of control over their reputation.
Key considerations
- DKIM signing strategy: ESPs must sign with their own domain for DKIM, which is essential for FBLs (e.g., Yahoo!) and other identification purposes. This doesn't prevent end-users from also signing with their own domains.
- Role of 5321.MAILFROM vs. 5322.FROM: The 5322.FROM is the visible From address, ideally what senders should DKIM sign with. The 5321.MAILFROM (return-path) is typically the ESP domain for bounce tracking, though some ESPs allow branding.
- Full whitelabeling: While senders can go to extreme lengths to fully white-label their traffic (own 5321.MAILFROM, DKIM, tracking domains), this isn't always essential unless dealing with a problematic ESP. The focus should be on choosing a good ESP.
- Sender practices are key: Ultimately, the sender's own practices, including list hygiene, content relevance, and engagement rates, are paramount for maintaining good domain reputation and deliverability, regardless of the IP type. Learn how hard bounce rates impact reputation.
Expert view
Deliverability expert from Email Geeks clarified that sending reputation is derived from multiple data points, including the DKIM signing domain, sending IPs, and the 5322.FROM domain, but typically not the 5321.MAILFROM domain. This distinction is crucial for understanding which elements truly influence deliverability.
Expert view
Deliverability expert from Email Geeks explained that shared IPs mean reputation is only as good as the worst sender in the pool. However, a good sender's strong overall practices can sometimes enable them to survive on a poorly reputed shared IP, due to other positive reputation signals.
What the documentation says
Official documentation and research often delve into the technical specifications and recommendations that govern email sending and reputation. They outline the roles of different email headers and authentication protocols (like DKIM and SPF) in establishing sender identity and trustworthiness. This foundational knowledge is critical for ESPs to design systems that support good deliverability and for senders to understand how their email is perceived by receiving mail servers.
Key findings
- RFC 5322 vs. RFC 5321: The 5322.From (header From) domain is what users see, while the 5321.MAILFROM (envelope From/return-path) domain is used for bounce handling. Mailbox providers assess reputation based on both, but often heavily weigh the 5322.From for user-facing reputation.
- DKIM alignment importance: For strong authentication and positive reputation, the domain used for DKIM signing should align with the 5322.From domain. This provides a clear and verifiable sender identity. More on DMARC, SPF, and DKIM.
- Tracking domain security: Documentation often recommends that all domains referenced within an email (including tracking and image hosting domains) should be controlled by the sender or a trusted party. Using unbranded or third-party shared domains for these elements can introduce reputational risks if those domains are compromised or poorly managed.
- Feedback loops (FBLs): ESPs need to be able to receive FBLs to monitor complaint rates effectively. Many FBLs (e.g., Yahoo!) are DKIM-based, requiring the ESP to sign with a domain they control for reporting purposes.
Key considerations
- Holistic reputation: Mailbox providers utilize a sophisticated blend of IP reputation, domain reputation (across multiple domains in the email), and authentication results to determine inbox placement. A weakness in any area can negatively impact the overall sender score.
- Sender authentication: Robust implementation of SPF, DKIM, and DMARC is fundamental. While ESPs manage the IP reputation, proper domain authentication falls largely on the sender, even when using an ESP. This contributes significantly to overall trustworthiness.
- Shared IP management by ESP: ESPs should rigorously monitor shared IP pools to quickly identify and mitigate the impact of malicious or negligent senders. This proactive management helps protect the collective reputation of the pool and benefits all senders using it.
- Customer branding options: ESPs are encouraged to offer customers the ability to use their own domains for 5321.MAILFROM and tracking, even if on shared IPs. This enables senders to consolidate their reputation under their own brand, providing more control and clarity.
Technical article
Official RFC documentation defines the 5322.From as the human-readable From address in the email header. It is the domain that ideally should be aligned with the DKIM signature for strong authentication and sender reputation.
Technical article
Official RFC documentation specifies the 5321.MAILFROM as the envelope sender address, commonly known as the Return-Path. This address is primarily used by the receiving server for sending bounce messages back to the sender.
Related resources
15 resources
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