Why would an ESP send unsolicited emails through a competitor?

An ESP might attempt this to bypass their own strict deliverability policies, avoid damaging their primary sending reputation, or target competitors' client bases with cold outreach. However, this is a highly unethical and risky maneuver.

How does sending unsolicited emails impact an ESP's own reputation?

Sending unsolicited emails significantly harms the ESP's own sender reputation, even if using a third party. This can lead to their primary domains or IPs being blocklisted (blacklisted), causing widespread deliverability issues for all their clients. Mailbox providers track sending behavior across all associated IPs and domains.

What legal risks are involved in sending unsolicited marketing emails?

Sending emails without proper consent violates international anti-spam laws like CAN-SPAM, GDPR, and CASL. This can result in significant legal fines, lawsuits, and damage to the company's public image and trustworthiness.

Can an ESP get blocklisted for sending unsolicited emails?

Yes, both the originating ESP's domains and the IP addresses of the third-party ESP used for sending can be added to public and private blocklists. This prevents emails from reaching inboxes across major ISPs, severely impacting deliverability for legitimate campaigns.

How can a legitimate sender avoid being affected by others' unsolicited email practices?

Legitimate senders can protect themselves by rigorously adhering to consent-based practices, maintaining excellent list hygiene, and monitoring their sender reputation and email authentication. Choosing an ESP with a strong reputation and clear anti-spam policies is also vital to avoid shared IP pool contamination.

What are the issues with ESPs sending unsolicited marketing emails through other ESPs? - Sender reputation - Email deliverability - Knowledge base

It seems almost counterintuitive, but sometimes an email service provider (ESP) might engage in the practice of sending unsolicited marketing emails not through their own infrastructure, but through another ESP, perhaps even a competitor. This scenario raises significant questions about ethical conduct, industry standards, and the broader impact on email deliverability.

While it might seem like a way to circumvent their own reputation or policies, this approach creates a complex web of problems. These issues affect not only the sending entity and the unwitting third-party ESP, but also the overall trust and stability of the email ecosystem. Let's delve into the specific challenges and consequences of such a practice.

The ripple effect on sender reputation

Sending unsolicited email, regardless of which ESP is used, invariably damages the sender's domain reputation. Internet service providers (ISPs) and mailbox providers meticulously track sender behavior, and a sudden influx of unrequested messages, especially those marked as spam, signals bad practices. This negative signal can tarnish the entire domain's sending ability, making it difficult for even legitimate emails to reach the inbox. A damaged reputation is notoriously hard to rebuild, affecting all future campaigns.

Many ESPs utilize shared IP pools, meaning multiple senders share the same IP addresses. If one sender on a shared IP (even a misbehaving ESP using another ESP) sends unsolicited emails, it can negatively impact the deliverability of all other legitimate senders using those same IPs. This collective punishment highlights the interconnectedness of sender reputation. You can learn more about how shared IP pools and sending domains impact email sender reputation for ESPs.

From the recipient's perspective, receiving unwanted emails leads to frustration and a high likelihood of marking messages as spam. High spam complaint rates are a critical indicator to ISPs that a sender is not adhering to best practices, leading to aggressive filtering, including direct delivery to the spam folder or outright rejection. This is a core reason why spam emails affect sender reputation.

Legitimate email sending

Opt-in consent: Relies on explicit permission from recipients.
Reputation building: Fosters a positive sender reputation over time.
High engagement: Leads to better open and click-through rates.

Unsolicited email sending

No consent: Ignores recipient permission and privacy.
Reputation damage: Swiftly harms sender and IP reputation.
Low engagement: Results in high complaints and bounces.

Legal and ethical ramifications

Sending unsolicited marketing emails, particularly through a third-party ESP, opens the door to significant legal risks. Jurisdictions globally have stringent anti-spam laws, such as CAN-SPAM in the US, GDPR in Europe, and CASL in Canada. These laws generally require explicit consent, clear identification of the sender, and an easy unsubscribe mechanism. Failing to comply can result in hefty fines and legal action for both the originating sender and potentially the ESP that facilitated the sending. Understanding the consequences of sending emails without consent is crucial.

Beyond legalities, there's a clear ethical breach when an ESP, whose core business is to ensure reliable email delivery, engages in practices that undermine trust and industry best practices. Such actions erode confidence among other ESPs, ISPs, and the wider email community. It suggests a willingness to compromise the integrity of email channels for perceived short-term gains, which is damaging to the entire ecosystem.

One common source of unsolicited email is the use of purchased or unverified email lists. Many email service providers (ESPs) explicitly forbid the use of such lists due to their poor quality, high bounce rates, and the presence of spam traps. Sending to these lists, regardless of the ESP used, is a direct violation of most reputable ESPs' acceptable use policies and can lead to account termination. This is a key reason why purchased email lists cause deliverability issues and are not a best practice.

Best practices for email consent

Obtain explicit consent: Always get clear, affirmative opt-in before sending any marketing emails.
Provide easy unsubscribe: Include a prominent and functional unsubscribe link in every email.
Maintain clear records: Keep detailed logs of when and how consent was obtained.
Respect preferences: Offer options for recipients to manage their subscription types.

Technical deliverability challenges

Unsolicited emails are highly susceptible to being caught by spam filters. These filters use sophisticated algorithms to identify suspicious sending patterns, lack of engagement, and high complaint rates. Emails originating from an ESP sending through another ESP might trigger even more flags, as the authentication and sending patterns may appear inconsistent or spoofed to receiving mail servers. This often leads to messages being quarantined or sent directly to spam folders, effectively rendering the marketing effort useless.

Proper email authentication protocols such as SPF, DKIM, and DMARC are crucial for deliverability. When an ESP sends emails using another ESP's infrastructure, ensuring proper alignment of these records can become complicated. Misconfigurations, such as a DMARC verification failed error, can result in emails failing authentication checks, which is a major red flag for ISPs and will lead to lower deliverability. Here’s an example of an SPF record that might cause issues if not properly managed across multiple ESPs:

Example SPF recordDNS

v=spf1 include:sending-esp.com include:another-esp.net -all

This practice greatly increases the risk of being placed on email blocklists (also known as blacklists). These lists are maintained by organizations that track known spamming IPs and domains. If an ESP's domain or the IPs they use are associated with sending unsolicited email through a third-party, both the originating domain and the IPs of the facilitating ESP could end up on these lists. This can lead to all emails from those IPs or domains being rejected by major mail providers like

Microsoft and

Google, effectively halting all email communication. Learning what happens when your domain is put on a blocklist is important.

Maintaining trust and brand integrity

The act of sending unsolicited emails, especially through an unapproved third-party, severely damages the brand reputation of the originating ESP and the domain whose emails are being sent. Recipients who receive unwanted messages associate them with the sender's brand, leading to negative perceptions, unsubscribes, and spam complaints. This can quickly erode customer trust and lead to widespread disengagement with all future marketing efforts, including those that are legitimate and consented.

This practice also erodes the collective trust within the entire email ecosystem. ISPs and mailbox providers rely on ESPs to uphold responsible sending practices. When an ESP deliberately flouts these norms by sending unsolicited mail, particularly through a competitor, it signals a disregard for deliverability standards. This can lead to stricter filtering rules for all senders, increasing costs and complexity for legitimate marketers. Overall sending reputation and associated costs become bigger issues.

Blocklist Type	Impact on Email Deliverability	How to Avoid
Public Blacklists (e.g., Spamhaus)	Emails are blocked by a wide range of ISPs and mail servers that query these lists. Can cause widespread delivery failure. For more, see how email blacklists actually work.	Maintain strict opt-in, clean lists, and resolve complaints quickly. Monitor common blocklists.
Private Blacklists (ISP-specific)	Emails are blocked or sent to spam specifically by the ISP maintaining the list (e.g., Outlook, Yahoo, etc.). For example, if O365 marks emails as spam.	Utilize Postmaster Tools, adhere to sender guidelines, and manage bounce/complaint rates.
Internal ESP Blocklists	The ESP itself might internally block senders who violate their terms of service, leading to account suspension.	Comply with all ESP policies, especially regarding list hygiene and consent.

Views from the trenches

Email deliverability is a dynamic and interconnected field, and sometimes the best insights come from those directly navigating its complexities. We've gathered some perspectives from various practitioners in the email community to shed light on real-world experiences related to unsolicited email and ESP practices.

Best practices

Maintain strict consent practices for all mailing lists.

Monitor your sender reputation actively using tools like Google Postmaster Tools.

Implement robust email authentication including SPF, DKIM, and DMARC.

Segment your audiences carefully to ensure relevant content delivery.

Common pitfalls

Sending emails to purchased lists or unverified contacts.

Ignoring spam complaints and high bounce rates.

Failing to properly warm up new sending IPs or domains.

Using generic or misleading subject lines that trigger spam filters.

Expert tips

Consistently audit your email lists for engagement and remove inactive subscribers.

Actively respond to feedback loops from major mailbox providers.

Ensure your unsubscribe process is clear, simple, and functional.

Regularly review your email content for anything that might appear spammy.

Expert view

Expert from Email Geeks says: An ESP engaging in unsolicited email sending, especially through a competitor, offloads their reputation hit, which is a significant ethical concern.

June 2020 - Email Geeks

Marketer view

Marketer from Email Geeks says: It's worse when an ESP subcontracts sketchy traffic to a smaller ESP, implying a known bad practice.

June 2020 - Email Geeks

These insights underscore the critical importance of responsible email sending practices. Understanding the challenges and adopting proactive measures are key to achieving consistent inbox placement and building lasting sender reputation.

Ethical email practices

The practice of an ESP sending unsolicited marketing emails through another ESP is fraught with severe risks. While it may appear to offer a way to bypass internal policies or shift responsibility, the long-term damage to sender reputation, legal compliance, and overall deliverability far outweighs any short-term perceived benefits. It compromises the trust between senders, ESPs, and ISPs, making email marketing harder for everyone involved.

For sustained email marketing success, adherence to ethical sending practices, prioritizing consent, and maintaining a robust sender reputation are non-negotiable. Legitimate marketing relies on building trusted relationships with recipients, not on sending unwanted communications.