Summary
The overwhelming consensus among experts, email marketers, and documentation sources is that utilizing multiple subdomains for different email streams is a best practice for managing sender reputation and improving email deliverability. The core benefit lies in isolating reputation; a negative reputation on one subdomain is less likely to affect others, especially critical transactional emails. Experts recommend separating email types like transactional, marketing, and bulk onto distinct subdomains. While some caution against excessive subdomain use, especially for smaller senders or due to the risk of "subdomain hopping" being flagged as snowshoe spamming, separating concerns by subdomain is a generally accepted strategy. Utilizing recipient-recognizable branding when naming subdomains and implementing separate IP pools per subdomain is also advised.
Key findings
- Reputation Isolation: Subdomains isolate sender reputation, minimizing the impact of issues on one subdomain on others.
- Transactional Protection: Dedicated subdomains protect the deliverability of critical transactional emails from issues affecting other email streams (e.g., marketing).
- Policy Application: Subdomains enable the application of distinct email policies tailored to specific email types.
- Organizational Benefits: Subdomains help in organizing and categorizing different types of email traffic.
- Gmail Troubleshooting: Multiple subdomains can assist in isolating intermittent Gmail deliverability issues to specific email streams.
Key considerations
- Subdomain Hopping Avoidance: Avoid 'subdomain hopping' to circumvent reputation issues, as this could lead to blacklisting.
- Warm-up Requirements: Switching large email volumes to a new subdomain necessitates a warm-up period to establish sender reputation.
- Implementation Complexity: Managing multiple subdomains introduces increased complexity, requiring careful planning and monitoring.
- Snowshoe Spamming Risk: Excessive use of subdomains can be flagged as snowshoe spamming, potentially leading to domain blacklisting.
- Recipient Recognition: Choose subdomain names that are recognizable and trustworthy to recipients (e.g., a.alerts.domain.com).
- Scaling Appropriately: Small senders may not need multiple subdomains. Start with a single, well-managed subdomain and expand as necessary.
- Shared IP Pool Appearance: If multiple subdomains use the same IP addresses, it may look like a shared IP pool setup
What email marketers say
13 marketer opinions
The general consensus is that using multiple subdomains for different email streams is a beneficial practice for managing sender reputation and improving email deliverability. Segmenting email types, such as transactional, marketing, and bulk emails, onto separate subdomains helps isolate reputation issues, preventing deliverability problems from one email type from affecting others, particularly critical transactional emails. However, some caution against excessive subdomain use, especially for smaller senders, and warn about the risks of 'subdomain hopping,' which can lead to being flagged for snowshoe spamming. It's generally recommended to start with a well-managed subdomain and scale as needed.
Key opinions
- Reputation Isolation: Subdomains isolate email sending reputation. A negative reputation on one subdomain does not necessarily impact others.
- Transactional Protection: Using separate subdomains protects critical transactional emails from deliverability issues caused by marketing emails.
- Segmentation Benefit: Subdomains allow for independent management and monitoring of sender reputation for different email types.
- Scalability Consideration: Multiple subdomains might be overkill for smaller senders. Start with one well-managed subdomain and scale as the email volume justifies it.
- Gmail: Can help isolate intermittent issues with Gmail to a specific domain for easier troubleshooting.
Key considerations
- Subdomain Hopping: Avoid 'subdomain hopping' to evade reputation issues, as it can lead to being flagged as a spammer.
- Warm-up Phase: Failing over millions of emails to a new subdomain requires a warm-up phase to establish its reputation.
- Implementation Complexity: Managing multiple subdomains increases implementation complexity. Ensure the volume justifies the additional overhead.
- Snowshoe Spamming: Be careful not to create too many subdomains, or it will be considered snowshoe spamming which can lead to TLD being blocked.
- IP Pools: Consider dedicating IP pools for each subdomain.
Marketer view
Email marketer from SuperOffice suggests that to safeguard your email deliverability, segment your email traffic and sending IPs into separate subdomains to avoid sending email streams from the same domain. For example, you can send marketing newsletters from one subdomain and sales emails from another.
22 Nov 2022 - SuperOffice
Marketer view
Email marketer from StackExchange recommends using subdomains to segregate different types of emails. For example, use transaction.domain.com for transactional emails, marketing.domain.com for marketing emails, and so on. This helps to isolate reputation and prevent deliverability issues for one type of email from affecting others.
1 Dec 2024 - StackExchange
What the experts say
6 expert opinions
Experts generally agree that using multiple subdomains for different email streams offers benefits such as reputation isolation and enhanced deliverability. Separating email types (e.g., marketing, transactional) allows for isolated management of sender reputation. While high volume doesn't always necessitate numerous subdomains, it can help isolate Gmail issues. Experts recommend recipient-recognizable branding for subdomains and caution against failing all traffic to another subdomain if one is blocked. One expert also notes that, at a certain volume and configuration, multiple subdomains may be viewed as a shared IP pool.
Key opinions
- Reputation Isolation: Separate subdomains isolate reputation, limiting the impact of a poor reputation on one subdomain on others.
- Transactional Protection: Separating marketing and transactional email onto different subdomains protects critical transactional messages.
- Gmail Isolation: Using multiple subdomains can help isolate intermittent Gmail issues.
- Volume Flexibility: While high volume can be managed with fewer subdomains, multiple subdomains can still be beneficial.
Key considerations
- Recipient Recognition: Aim for recipient-recognizable branding when naming subdomains (e.g., a.alerts.domain.com instead of goldylocks.domain.com).
- Overload Avoidance: Avoid failing all traffic to another subdomain if one gets blocked; this could put the others at risk.
- Shared Pool Appearance: Using multiple subdomains from the same IPs can make it appear as a shared IP pool.
Expert view
Expert from Word to the Wise highlights that sending marketing and transactional email from the same domain or subdomain puts your critical transactional messages at risk. It is crucial to separate email streams using distinct subdomains to protect the reputation of your transactional email.
8 Aug 2021 - Word to the Wise
Expert view
Expert from Spam Resource explains that using separate subdomains isolates reputation. If one subdomain develops a bad reputation due to specific campaigns or user behavior, it's less likely to impact the deliverability of emails sent from other subdomains.
17 Feb 2024 - Spam Resource
What the documentation says
5 technical articles
The documentation sources consistently recommend using multiple subdomains for different email streams to improve organization, apply distinct policies, and isolate sender reputation. This approach protects critical transactional emails from deliverability issues associated with other types of email, such as marketing or promotional messages. The RFC Editor documentation provides the technical foundation for understanding the distinct nature and separate management of subdomains.
Key findings
- Organization: Subdomains help organize email by type, e.g., marketing.example.com vs. transactional.example.com.
- Policy Application: Different policies can be applied to different subdomains.
- Reputation Isolation: Dedicated subdomains prevent reputation issues with one email stream from affecting others.
- Transactional Protection: Using separate subdomains ensures high deliverability for critical transactional emails.
Key considerations
Technical article
Documentation from Google Workspace Admin Help explains that using subdomains can help organize email and apply different policies to different types of mail. For example, marketing emails can be sent from 'marketing.example.com' and transactional emails from 'transaction.example.com'.
27 Oct 2023 - Google Workspace Admin Help
Technical article
Documentation from Microsoft explains that sender reputation is tied to the domain/subdomain. Using dedicated subdomains for different mail streams can prevent issues with one stream from impacting the deliverability of other, more important email such as transactional messages.
12 Apr 2024 - Microsoft
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