Can negative sending on a synonym domain affect my main domain's reputation?

Yes, it can. Mailbox providers use advanced algorithms, including machine learning, to detect patterns in sender behavior. If multiple domains frequently send similar content or share infrastructure, filters may associate them, and negative activity on one can impact the others. This is also true if you are using the same sending domain across multiple platforms.

Why are subdomains a better choice than synonym domains for email deliverability?

Subdomains are generally safer because they inherit the sender reputation of the parent domain. This means you don't have to build a new reputation from scratch for each sending identity. They also provide clearer brand consistency and allow for better segmentation of email types without creating separate, potentially suspicious, top-level domains.

If all my synonym domains are authenticated, does that eliminate the risk?

While proper authentication (SPF, DKIM, DMARC) is essential, it's not a complete guarantee against deliverability issues. Filters look at a wide range of factors, including content, sender behavior, recipient engagement, and domain age. Even with authentication, if your domains exhibit suspicious patterns, they can still be flagged. You can learn more about DMARC, SPF, and DKIM from our guides.

Does the choice of top-level domain (TLD) for a synonym domain matter?

Some TLDs, particularly newer or less common ones, might be viewed with more suspicion by mailbox providers and recipients until they establish a strong reputation. Sticking to well-established TLDs like .com can offer an initial trust advantage, but ultimately, consistent positive sending behavior is the most important factor for any TLD.

Is it risky for deliverability to use several synonym domains that contain the main domain? - Sender reputation - Email deliverability - Knowledge base

The question of whether to use several synonym domains that contain your main domain, rather than subdomains, for email outreach is common in the deliverability world. While the intent might be to segment different activities or expand your digital footprint, it introduces several complexities and potential risks to your email deliverability and sender reputation.

I've seen many businesses explore this approach, especially those wanting to separate marketing initiatives or maintain distinct branding for different product lines. However, the path of using multiple, closely-named top-level domains (TLDs) can inadvertently trigger spam filters and even train your recipients to be less vigilant against phishing attacks.

The deliverability risk of synonym domains

Using multiple synonym domains, such as name-marketing.io or getname.ai, alongside your main domain like name.com, presents a significant deliverability risk. Even if all these domains are properly authenticated with SPF, DKIM, and DMARC, mail filters can still identify them as suspicious.

Modern email filters, especially those powered by machine learning (ML-based filters), are sophisticated. They look beyond basic authentication to assess sender legitimacy. When they see multiple domains that are phonetically or visually similar to a known brand's main domain, they may flag them as potential phishing attempts or spam.

This isn't just about technical authentication, it's about perception and behavior. Recipients might become confused by emails arriving from slightly different, yet similar, domain names. This confusion can lead to lower engagement, increased spam complaints, and a reduced likelihood of your emails being added to address books, all of which negatively impact your sender reputation. A damaged sender reputation can take considerable time to restore. You can learn more about how to recover domain reputation.

The primary problem

Using synonym domains can inadvertently train your recipients to trust lookalike domains, making them more vulnerable to actual phishing attacks. This erodes trust and can lead to serious security incidents for your customers. Your domain name directly affects deliverability. If it looks suspicious, your emails might not reach the inbox.

How mail filters connect domains

Mailbox providers (MBPs) employ sophisticated techniques to identify related domains, even if they aren't technically subdomains. This helps them combat phishing and spam more effectively. It's not just about the technical authentication, but also the behavioral patterns and contextual signals.

Sender behavior: If multiple domains send similar content to the same recipient lists, especially with low engagement, filters will likely connect them. This often happens with cold outreach campaigns using lookalike domains for sales.
Content analysis: Shared content, links pointing to the same web properties, or consistent branding across different domains can signal a connection to filters. Consistent branding also reduces the risk of being seen as spam by email providers.
Shared infrastructure: If multiple synonym domains share the same sending IPs or mail servers, filters can easily tie them together. You should also consider deliverability issues with multiple email addresses from the same domain and IP.
WHOIS data: Shared registrant information in WHOIS records (though often masked with privacy services) can also be a linking factor.

The danger lies in the potential for any negative activity on one of these cousin domains to impact the reputation of your entire domain portfolio, including your main domain. This is why using subdomains is often recommended, as they inherit the reputation of the parent domain and allow for better segmentation without introducing new top-level reputation challenges.

Subdomains versus synonym domains

Synonym domains (cousin domains)

Each synonym domain (name-marketing.io, getname.ai) starts with a fresh, independent sender reputation. This means you have to build trust from scratch for each one. This can be challenging for multiple or external domains.

Phishing risk: Increases the chance of being flagged as a phishing attempt due to visual similarity to your main domain.
Recipient confusion: Can confuse recipients, leading to lower open rates, fewer clicks, and more spam complaints. This is true for any different domains used in email addresses.
Brand inconsistency: Dilutes your brand consistency and can lead to a fragmented sender identity.
Blacklisting risk: If one synonym domain gets blocklisted (blacklisted), it can potentially drag down the reputation of others if filters see them as connected.

Subdomains

Subdomains (marketing.name.com, network.name.com) inherit the reputation of your main domain, name.com. This provides a solid foundation for deliverability, while still allowing for segmentation.

Reputation leverage: Subdomains benefit from your established primary domain reputation, making it easier to achieve good inbox placement. You can also control whether a subdomain impacts the primary domain's reputation.
Segmentation: Allows you to separate different email streams (transactional, marketing, cold outreach) onto distinct subdomains. This isolates potential issues, so if one subdomain encounters problems (e.g., gets blacklisted), it's less likely to affect others or your main domain. This is important for protecting your main domain reputation.
Clear identity: Maintains a clear and consistent brand identity in the eyes of recipients, reducing confusion and increasing trust.
Easier management: Simpler to manage DNS records and authentication for subdomains under a single root domain.

When deciding on your domain strategy, I always advise prioritizing clarity and trustworthiness for your recipients. Subdomains achieve this far better than a scattered approach with multiple synonym domains. A consistent sender identity is a cornerstone of strong deliverability.

One area where this is particularly important is with country code top-level domains (ccTLDs) or newer generic TLDs (gTLDs). While .com domains often carry inherent trust, other TLDs, especially those less commonly associated with business operations (like .io for example), might face more scrutiny from spam filters or be perceived as less legitimate by recipients. If you're considering using a non-standard TLD, be prepared to work harder to build and maintain its reputation.

Best practices for domain management

To protect your email deliverability, focus on building a strong, consistent sender reputation around your main domain and leveraging subdomains for segmentation. This approach minimizes the risk of being flagged as suspicious and helps maintain recipient trust.

Regular monitoring of your domain reputation, using tools like blocklist checkers, and analyzing your DMARC reports are critical steps. These insights will help you quickly identify and address any issues that arise, preventing them from escalating and affecting your ability to reach the inbox. You can also explore technical solutions for better deliverability.

Views from the trenches

Best practices

Always use subdomains for separating email types (e.g., transactional, marketing, cold outreach) to centralize reputation.

Ensure all sending domains and subdomains are properly authenticated with SPF, DKIM, and DMARC.

Maintain consistent branding across all your email communications, regardless of the sending domain or subdomain.

Common pitfalls

Using visually similar or 'cousin' domains, which can be perceived as phishing attempts by both filters and recipients.

Not having consistent sender behavior across different domains, leading filters to flag them as suspicious.

Failing to monitor engagement metrics for each sending domain or subdomain, missing early signs of deliverability issues.

Expert tips

If you must use multiple top-level domains, ensure they serve distinct, clear purposes and are explicitly communicated to your audience.

Consider the long-term impact on recipient trust and brand perception when choosing your domain strategy.

Prioritize consistent sender authentication and a clean sending history for all domains under your brand.

Marketer view

Marketer from Email Geeks says that if the content you are sending is unexpected or unwanted, ML-based filters may connect all logically related domains.

2022-02-24 - Email Geeks

Marketer view

Marketer from Email Geeks says that using subdomains is a better approach for separating different email activities.

2022-02-24 - Email Geeks

A clear path to better deliverability

While the temptation to use multiple, closely-named domains for various brand activities might seem appealing, the deliverability risks often outweigh the perceived benefits. Email service providers and mailbox providers are increasingly vigilant against anything that resembles phishing or spam, and a scattered domain strategy can easily trigger these defenses.

My advice is to consolidate your email sending under your primary domain and its subdomains. This approach provides a clearer brand identity, leverages your established reputation, and simplifies your deliverability management. Prioritizing sender reputation and recipient trust will always be the most effective strategy for reaching the inbox consistently.