Summary
Allowlisting domains for email sending can significantly improve deliverability by bypassing spam filters and ensuring important messages reach their intended recipients. However, it is a practice that comes with inherent risks if not handled with caution. Simply adding a top-level domain or a wildcard for all subdomains to an allowlist without robust authentication (like DMARC) can inadvertently open the door to phishing and spoofing attacks, making it crucial for organizations to understand the technical implications.
Key findings
- Controlled access: Allowlisting is used to grant specific senders a 'free pass' through email protection defenses, ensuring their emails are not quarantined or sent to spam folders.
- Subdomain management: When using multiple subdomains for email sending, it is often necessary to explicitly list each one or confirm if wildcard allowlisting (e.g., *.company.com) is supported by the recipient's system to prevent oversight.
- Authentication dependency: Allowlisting should ideally only occur if the sending domain is fully authenticated and verified, specifically through the implementation and validation of DMARC, in addition to SPF and DKIM.
- From field importance: Many allowlisting mechanisms rely on the domain found in the visible 'From:' field of an email, rather than the domains verified by SPF or DKIM directly.
Key considerations
- Security risk: Blindly allowlisting domains without robust authentication can render organizations vulnerable to spoofing, phishing, and other malicious email activities.
- DMARC for trust: A valid DMARC policy, alongside SPF and DKIM, is crucial to assure recipients that emails from a given domain are legitimate and not spoofed, making allowlisting safer.
- Communication clarity: When providing allowlisting instructions to clients, it is important to be explicit about all sending domains and subdomains, and to clarify the role of email authentication. For more details, consider Higher Logic's allow-listing tips for marketers.
- Subdomain impact: Understanding how subdomains affect sender reputation is essential before instructing clients on allowlisting practices, as each subdomain can have its own reputation.
What email marketers say
Email marketers often seek ways to ensure their campaigns reliably land in the inbox, leading them to consider allowlisting. While it seems like a straightforward solution, marketers frequently grapple with the technical nuances, such as whether to specify individual subdomains or rely on wildcards. Their primary goal is to provide clear, actionable instructions to clients' IT teams, balancing technical accuracy with ease of understanding, all to bypass spam filters and improve inbox placement.
Key opinions
- Deliverability focus: Marketers prioritize allowlisting to prevent emails from being quarantined or sent to spam, especially when dealing with important client communications.
- Subdomain clarity: There's a strong desire to simplify allowlisting instructions for multiple sending subdomains, often hoping that wildcards like *.company.com will suffice.
- Ease of implementation: Marketers look for simple, straightforward steps for client IT teams to implement allowlisting, minimizing complexity.
- Authentication understanding: Many marketers are aware of SPF and DKIM but seek further guidance on what 'fully authenticated and verified' truly means for allowlisting, highlighting a gap in technical understanding.
Key considerations
- Explicit subdomain listing: While wildcards are convenient, explicit listing of all sending subdomains may be necessary to avoid misconfigurations by recipient IT teams, ensuring all legitimate emails are received.
- Comprehensive authentication: Marketers should not assume a domain will be allowlisted purely for deliverability without confirming that strong email authentication protocols, including DMARC, are in place and correctly configured. This aligns with Twilio's guide on allowlists.
- Recipient education: Educating clients about the risks of allowlisting unauthenticated domains is crucial for maintaining both sender and recipient security.
- Domain reputation: Consistent positive sending practices, which contribute to a strong healthy domain reputation, reduce the overall need for recipients to manually allowlist domains.
Marketer view
A marketer from Email Geeks explains their initiative to create an allowlist document for partnered clients, aiming to ensure email deliverability and prevent messages from being quarantined or routed to spam, especially given their use of multiple sending subdomains.
Marketer view
An email marketer from Higher Logic emphasizes that strategic allowlisting is a vital practice for email marketers to circumvent spam filters, thereby ensuring that their emails consistently achieve inbox placement and reach their intended audience.
What the experts say
From an expert perspective, allowlisting is a powerful tool for deliverability, but its application must be strictly governed by robust email authentication. Experts emphasize that simply allowlisting a domain based on the 'From:' address without verifying its authenticity through DMARC, SPF, and DKIM creates a significant security vulnerability, as it can allow spoofed emails to bypass security measures. The consensus is that allowlisting should only be considered as a last resort or for highly trusted, thoroughly authenticated senders.
Key opinions
- Conditional allowlisting: Domains should only be allowlisted if they are fully authenticated and verified by protocols like DMARC.
- Spoofing risk: Without proper authentication, allowlisting can inadvertently legitimize spoofed emails, posing a significant security threat.
- DMARC is key: DMARC is highlighted as critical for domain authentication, as SPF and DKIM alone do not directly validate the visible 'From:' field.
- Trust through authentication: Building trust through robust authentication practices like DMARC, SPF, and DKIM reduces the need for recipients to manage allowlists manually.
Key considerations
- Prioritize authentication: Senders should focus on implementing and enforcing strong email authentication protocols rather than relying solely on recipients to allowlist their domains.
- Security implications: Organizations should be fully aware of the heightened security risks associated with allowlisting domains that lack proper DMARC enforcement.
- Education on 'from' field: It's important to educate recipients that allowlisting often targets the visible 'From:' domain, and therefore, this domain must be protected by authentication. More information can be found on Word to the Wise's insights regarding email best practices.
- Alternatives to allowlisting: For ongoing deliverability, focusing on email best practices and maintaining a strong sender reputation is more sustainable than relying on constant allowlisting requests.
Expert view
An expert from Email Geeks strongly advises against allowlisting domains without complete authentication and verification, highlighting that such practices create significant security vulnerabilities that can be exploited for malicious purposes.
Expert view
An expert from SpamResource cautions that implementing broad domain allowlists without stringent authentication checks can inadvertently expose an organization to increased risks of phishing attacks, malware distribution, and other forms of email-borne threats.
What the documentation says
Official documentation from various platforms and service providers consistently outlines allowlisting as a method to ensure email delivery by bypassing security filters. However, a common thread in technical documentation is the emphasis on the distinction between allowlisting and proper email authentication. Documentation suggests that allowlists are primarily about explicit permission, but true deliverability and security are best achieved when senders adhere to industry-standard authentication protocols, rather than relying solely on recipient-side configurations.
Key findings
- Permission-based delivery: Allowlisting is defined as a process that explicitly grants permission for emails to be delivered from specific addresses, domains, or networks.
- Bypassing filters: The core purpose of an allowlist is to ensure that desired emails are sent to the primary inbox and bypass standard spam filtering mechanisms.
- Complement to blocklists: Allowlists are often discussed in contrast to blocklists, serving to manage incoming email traffic by explicitly permitting trusted sources.
- Configurable domains: When allowlisting by domain, documentation typically instructs users to include the specific email server domain configured for sending.
Key considerations
- Internal domain allowlisting: Some documentation advises against adding an organization's own domain to an internal allowlist, noting that internal spam filtering often relies on content, not just the sender.
- Authentication best practices: While allowlisting can help, the foundational recommendation from documentation is for senders to implement robust authentication (SPF, DKIM, DMARC) for reliable deliverability. For more on this, consult IONOS Digital Guide.
- Scoped allowlists: Allowlists can be configured for specific purposes, such as restricting internal collaboration to a list of approved email domains.
- Avoiding bypass risks: Documentation often implies that allowlisting effectively grants a 'free pass,' emphasizing the importance of only allowlisting truly trusted sources to avoid bypassing critical security defenses that email blocklists aim to enforce.
Technical article
Barracuda Campus documentation advises that when configuring an email allowlist by domain, it is critical to precisely include the specific email server domain that is being used for outgoing mail to ensure proper recognition and delivery.
Technical article
Zendesk help elucidates that allowlists are instrumental for explicitly permitting emails from specific domains or individual email addresses, and are often employed in conjunction with blocklists to create comprehensive inbound email management rules.
Related resources
14 resources
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