Is it better to create a new, unique sender for each client project?

Isolating each project on a new, unique sender (subdomain and IP) is generally not recommended. Email reputation takes time to build, and constantly spinning up new senders prevents the accumulation of positive sending history. This can lead to persistent warming-up phases and hinder overall deliverability. It also removes incentives for clients to maintain good sending practices.

What are the risks of using shared IP addresses and subdomains for clients?

Shared IP addresses and subdomains mean that one client's poor sending habits can negatively impact the reputation of the entire shared infrastructure, affecting all other clients. This is known as the "bad neighborhood" effect. Robust vetting, monitoring, and enforcement of email best practices are crucial to mitigate this risk.

What proactive steps can I take to protect my platform's sender reputation?

Implement strong email authentication (SPF, DKIM, DMARC), enforce list hygiene and email validation, and actively monitor client-specific metrics like bounces and complaints. Provide content guidelines and consider automated content scanning for custom emails. Educate clients on how their sending behavior affects deliverability.

Do transactional emails impact sender reputation?

Yes, even transactional emails contribute to sender reputation. While their open and click rates are typically high, improper configuration, high bounce rates from invalid addresses, or unexpected spikes in volume without warming can still negatively impact your reputation. Ensure proper authentication and list management even for transactional streams.

How does email volume per client affect the choice of sending infrastructure?

If clients are sending high volumes, dedicated IPs and subdomains per client (or per group of similar clients) might be necessary to isolate reputation. For lower volumes, shared infrastructure with strict compliance and monitoring can work. The key is to manage the volume and behavior on each sending identity appropriately.

How should I manage sender reputation when clients send emails through my platform? - Sender reputation - Email deliverability - Knowledge base

When building a platform that allows clients to send emails, managing sender reputation becomes a critical responsibility. The choices you make regarding your email infrastructure, such as shared versus dedicated IPs and subdomains, directly impact the deliverability of all emails sent through your system. A single client's poor sending practices can negatively affect the reputation of your entire platform, leading to reduced inbox placement for everyone.

The initial thought might be to isolate each client or even each project with its own unique sender, like a dedicated subdomain and IP. While this approach seems to contain potential reputation issues, it introduces its own set of challenges, particularly around the crucial process of email warming and consistent sending volume. Reputation is built over time with consistent, positive sending behavior.

This guide explores effective strategies for managing sender reputation in a multi-client email sending environment, ensuring high deliverability for all users on your platform.

Client segmentation vs. shared infrastructure

A common dilemma for platforms is deciding between isolating sender reputation per client or sharing a common sending infrastructure. The allure of isolating each client on their own subdomain and IP is the belief that a bad actor will only harm their own sending reputation, leaving others untouched. However, this strategy often overlooks the significant effort required to build and maintain reputation.

Email reputation is not instantly established. It requires a consistent history of sending desired emails, low complaint rates, and high engagement. If each client, or even each project within a client, uses a new, unique sender, then every new sending identity will need to go through a warming-up period. For clients with low sending volumes, this can be a perpetual challenge, as their sender reputation may never fully mature. This approach can also make it harder for your platform to enforce good sending behaviors.

Conversely, using a shared subdomain and IP address for multiple clients means that the sending practices of one client can affect the deliverability for all others. While this presents a greater risk, it also incentivizes strict vetting and monitoring processes. Often, for platforms with moderate sending volumes per client, a balance is struck, such as grouping clients by industry or type on specific subdomains to manage risk and build more robust, shared reputations. You can learn more about managing your IP reputation.

Fundamentals: Authentication, content, and engagement

A cornerstone of good sender reputation is strong email authentication. This includes properly configuring SPF, DKIM, and DMARC records for all sending domains and subdomains. These protocols verify that your emails are legitimate and prevent spoofing, which is crucial for building trust with mailbox providers like

Gmail and

Outlook. Without these, even well-intentioned emails may land in spam folders or be rejected outright.

Beyond technical setup, content quality and recipient engagement are paramount. Mailbox providers assess your sender reputation based on how recipients interact with your emails, including open rates, click-through rates, and, importantly, complaint rates and unsubscribe rates. Providing clients with tools to create relevant, engaging content and segment their audiences is key to fostering positive engagement. High bounce rates, especially hard bounces, signal poor list hygiene and significantly harm reputation. Regularly verifying email lists is essential.

Another crucial aspect is monitoring for spam traps. Sending to spam traps immediately flags you as a risky sender and can lead to your IPs or domains being added to email blacklists (or blocklists). Implement stringent list cleaning protocols and educate clients on the dangers of purchased or unverified email lists. The goal is to ensure only recipients who have explicitly opted-in receive emails, a practice known as permission-based sending.

Client content and compliance management

One of the biggest risks when clients send emails through your platform is the content they choose to send. Even if most emails are transactional (like application confirmations or interview invitations), allowing clients to create their own custom email templates introduces an element of unpredictability. Unvetted content can contain spammy keywords, broken links, or misleading information, all of which can trigger spam filters and damage your sender reputation (or blocklist standing).

To mitigate this risk, implement content scanning mechanisms, perhaps using AI to flag potentially harmful or low-quality content before it's sent. Provide clear guidelines and best practices for email content to your clients, emphasizing the importance of relevance, clarity, and avoiding spam trigger words. Educate them on how their content choices directly impact their email deliverability and your platform's overall reputation.

Beyond content, strict compliance infrastructure is non-negotiable. This includes robust email validation processes to prevent sending to invalid addresses and mechanisms to detect and handle bounces effectively. Ensuring that all emails include a clear and functional List-Unsubscribe header is also vital for compliance with major mailbox providers and maintaining a positive sender reputation. Actively monitoring complaint rates and proactively addressing client issues are key to preventing widespread deliverability problems across your platform.

Monitoring and strategic grouping

When clients use your platform, consistent monitoring of their sending behavior is crucial. This means tracking metrics like open rates, click-through rates, bounce rates, and complaint rates at a client-specific level. Promptly address any spikes in negative metrics, as they can be early warning signs of reputation issues. Consider implementing automated alerts that notify you when a client's sending behavior deviates from acceptable norms.

For transactional platforms, like a hiring platform, even though email volume per client might be relatively low (e.g., 5,000-10,000 sends per month), the cumulative effect across all clients on shared IP addresses can be significant. If you cannot afford dedicated IPs and subdomains per client, grouping clients by industry sector (e.g., sales, marketing, tourism) or organizational size (e.g., enterprise, SME, startup) can help manage subdomain reputation. This strategy allows for more effective reputation management within segmented groups, mitigating the bad neighborhood effect.

Ultimately, the key is to prioritize the long-term health of your platform's sender reputation. This means educating clients on best practices, enforcing compliance, and having robust monitoring and remediation processes in place. A strong reputation ensures that all clients benefit from high deliverability, fostering trust and success for everyone involved.

Views from the trenches

Best practices

Implement stringent email validation and list cleaning to minimize bounces and protect your sender score.

Enforce email authentication protocols (SPF, DKIM, DMARC) for all client-sending domains.

Educate clients on email best practices, including content quality and list hygiene.

Common pitfalls

Allowing clients to upload unvetted email lists without any verification processes.

Using short-lived or disposable sender identities for each project, hindering reputation buildup.

Failing to enforce clear guidelines for client content, leading to spammy messages.

Expert tips

Consider grouping clients by industry or sending volume on specific subdomains to manage shared reputation risks.

For custom content, implement AI-driven content scanning to flag problematic emails before sending.

Ensure all emails, including transactional ones, include a functional List-Unsubscribe header for recipient control.

Expert view

Expert from Email Geeks says that reputation takes time to build, so using persistent mail streams is better for maintaining a good reputation. Isolating each new project means it will always look like a new sender and have to warm up repeatedly.

July 19, 2024 - Email Geeks

Expert view

Expert from Email Geeks says that for significant email volumes, you will need to warm up each individual subdomain every time you spin one up. It is also crucial to have compliance infrastructure to prevent customers from sending spam.

July 19, 2024 - Email Geeks

Ensuring deliverability across your platform

Managing sender reputation when clients use your platform is a complex but essential task. It requires a multifaceted approach that combines robust technical configurations with proactive client management and continuous monitoring. The goal is to create an environment where good sending practices are encouraged and rewarded, while problematic behaviors are quickly identified and corrected. Improving your overall email deliverability is paramount to client success and platform stability.