Should I be concerned about spoofing when using a different from domain than the subdomain configured in the ESP?
Matthew Whittaker
Co-founder & CTO, Suped
Published 8 Jun 2025
Updated 16 Aug 2025
8 min read
It is a common scenario in many organizations for different teams to use various email sending platforms (ESPs). While marketing might use one platform for campaigns, customer success or transactional emails could be sent from another. A question often arises when teams deviate from the subdomain explicitly configured in their ESP and start using a different "from" domain for their communications. This raises valid concerns about email spoofing and potential deliverability issues.
My concern is rooted in understanding how email authentication protocols like SPF, DKIM, and DMARC interact with multiple sending domains and subdomains. If these protocols are not correctly configured across all sending sources, even minor deviations in the "from" address can be misinterpreted by recipient mail servers as attempts to spoof your domain. This can lead to emails being marked as spam or outright blocked, damaging your sender reputation.
Ensuring proper authentication is key to preventing such problems. It is not just about having SPF, DKIM, and DMARC records, but also about making sure they align correctly with the domains used in the "from" header, the "mailed-by" field, and the DKIM signature. The slightest mismatch can put your emails at risk of failing authentication checks, which is why a proactive approach to monitoring and configuration is essential.
When an ESP is configured, it typically uses a specific subdomain (e.g., m.yourdomain.com) for sending emails. This subdomain is where the SPF and DKIM records are configured to authorize the ESP's sending IP addresses and sign emails. The "from" header domain (the one recipients see) is often your main domain or a related subdomain (e.g., yourdomain.com). The key is that SPF and DKIM authentication must align with the From header domain.
When a different "from" domain is used—one that isn't properly configured for authentication within the ESP or for which no dedicated authentication is set up—it creates a discrepancy. Recipient mail servers, especially those of major providers like Google and Microsoft, strictly check for SPF and DKIM alignment, alongside a strong DMARC policy. If SPF fails or if the DKIM signature doesn't match the "from" domain, the email's legitimacy comes into question.
The primary goal of these authentication protocols is to prevent unauthorized entities from sending emails pretending to be from your domain (spoofing). A comprehensive guide to implementing SPF, DKIM, and DMARC stresses the importance of proper setup for all sending sources. When the "mailed-by" domain (SPF's domain) and the DKIM signing domain do not align with the "from" domain, it creates an authentication gap that can lead to deliverability issues, even if the email technically passes SPF or DKIM individually.
Understanding email authentication
Email authentication protocols verify sender identity to prevent phishing and spoofing. They ensure the email originates from the domain it claims to be from.
SPF (Sender Policy Framework): Verifies the sender's IP address against a list of authorized IPs in the domain's DNS record.
DKIM (DomainKeys Identified Mail): Adds a digital signature to the email header, allowing the recipient server to verify that the email content hasn't been tampered with and was sent by an authorized sender.
DMARC (Domain-based Message Authentication, Reporting, and Conformance): Builds on SPF and DKIM, providing a policy framework for how recipient mail servers should handle emails that fail authentication. It also provides reporting capabilities.
The risk of spoofing and authentication failures
When your Customer Success team sends emails using a "from" domain that isn't aligned with the ESP's configured subdomain or its authentication records, you absolutely should be concerned. This mismatch significantly increases the risk of those emails being flagged as suspicious. Recipient mail servers are designed to detect and filter out emails that appear to be spoofed, even if unintentionally. This can lead to your emails landing in the spam folder or being rejected entirely, severely impacting your communication efforts.
DMARC, in particular, relies heavily on alignment. For an email to pass DMARC, either the SPF domain or the DKIM domain must align with the "from" header domain. If your Customer Success team's chosen "from" domain doesn't match either the SPF (return-path) domain or the DKIM (signed-by) domain, then DMARC authentication will fail. This failure sends a strong signal to receiving mail servers that the email may be fraudulent, triggering their spam filters and potentially causing your domain to be added to a blocklist (or blacklist).
This situation can also degrade your sender reputation over time. Even if initial emails manage to get through, consistent authentication failures will lead to lower inbox placement rates. It’s crucial to understand why subdomains should not inherit the SPF policy of the parent domain, as this is a common misconfiguration that can open doors to spoofing risks.
Non-aligned domains (risky)
From header:team@customersuccess.com
SPF (mailed-by):esp.yourdomain.com
DKIM (signed-by):esp.yourdomain.com
Potential outcomes
DMARC failure: Emails are more likely to fail DMARC alignment checks, even if SPF/DKIM pass individually.
Spoofing flags:Recipient mail servers (e.g., Gmail, Outlook) may classify these emails as spoofed.
Reduced deliverability: Higher chance of landing in spam folders or being outright rejected. Increased risk of blocklisting.
Aligned domains (best practice)
From header:team@yourdomain.com
SPF (mailed-by):esp.yourdomain.com
DKIM (signed-by):yourdomain.com (or esp.yourdomain.com, if configured)
Desired outcomes
DMARC pass: Emails pass DMARC checks due to SPF or DKIM alignment.
Trust and reputation: Improved sender reputation and recipient trust.
High deliverability: Emails consistently reach the inbox, avoiding spam folders and blacklists.
Practical steps to ensure proper authentication
To address these concerns, the first step is to thoroughly examine the authentication headers of emails sent by the Customer Success team. You can do this by viewing the original message in your email client, which reveals the SPF (often seen as "mailed-by" in Gmail) and DKIM (signed-by) domains. The goal is to verify if these domains align with the "from" header domain. If they don't, you'll need to adjust your DNS records to authorize that specific "from" domain within your ESP's sending configuration, or use a "from" address that matches the ESP's sending domain.
For scenarios where you use multiple ESPs or sending services, it's essential to configure SPF and DKIM for each one, ensuring that they properly authenticate all variations of your "from" domains. For instance, if "yourdomain.com" is used as the "from" address across different platforms, all platforms must be authorized to send on behalf of "yourdomain.com" in your SPF record, and sign with "yourdomain.com" in DKIM. This might involve adding include mechanisms to your SPF record or setting up CNAMEs for DKIM selectors provided by your ESPs.
Furthermore, implementing a DMARC policy with a p=quarantine or p=reject policy provides an additional layer of protection, instructing recipient servers what to do with unauthenticated mail purporting to be from your domain. For guidance on setting up these policies, Google's email sender guidelines are an excellent resource.
Example email headers for authentication checktext
Received: from [sending_ip]
by [receiving_server] with ESMTPS id [message_id]
for <recipient@example.com>;
[date]
Authentication-Results: mx.google.com;
spf=pass (google.com: domain of bouncing@esp.com designates [sending_ip] as permitted sender) smtp.mailfrom=bouncing@esp.com;
dkim=pass header.i=@yourdomain.com header.s=s1 header.b=abcdefgh;
dmarc=pass (p=quarantine dis=none) header.from=yourdomain.com
From: Your Name <info@yourdomain.com>
Subject: Your Email Subject
If SPF and DKIM authentication are not correctly configured, mail servers may consider the emails as unauthenticated or suspicious, increasing the likelihood of them being routed to the spam folder. This is especially true if a DMARC policy is in place for your root domain with a restrictive policy, such as p=reject. It is vital to confirm that your email service provider is correctly handling the DKIM signing for the specific "from" domain being used. When the signed-by domain doesn't match the "from" domain, it can lead to DMARC alignment failures, even if DKIM technically passes.
In essence, ensuring that all sending domains and subdomains have their SPF and DKIM records properly configured, and that they align with your DMARC policy, is the most robust way to protect against spoofing and maintain optimal email deliverability. This includes coordinating with all teams and platforms that send emails on behalf of your domain to prevent unintended authentication failures.
Best practices for multi-platform sending
Audit sending sources: Identify every platform sending emails using your domain or subdomains. This includes marketing, transactional, and customer service ESPs.
Centralized DNS management: Ensure you have control over your domain's DNS to implement and update authentication records effectively.
Consistent SPF, DKIM, DMARC: Set up and monitor these records for every sending domain and subdomain to ensure proper alignment.
Subdomain strategy: Consider using specific subdomains for different types of email (e.g., marketing, transactional) to isolate reputation.
Ensuring email authenticity and deliverability
In conclusion, using a different "from" domain than the subdomain configured in your ESP is a legitimate concern. While it might not immediately lead to deliverability issues, it creates a vulnerability that can be exploited for spoofing or trigger stringent spam filters.
The key to mitigating this risk lies in ensuring all your email sending practices adhere to strong authentication standards, particularly DMARC alignment. Proactive monitoring of your email authentication status and strict adherence to best practices for SPF and DKIM across all sending platforms will safeguard your domain's reputation and ensure your emails reach their intended recipients reliably.
Views from the trenches
Best practices
Ensure full control over your domain's DNS for complete authentication setup.
Implement DMARC with a policy (e.g., quarantine or reject) to enforce email authentication.
Verify that both SPF and DKIM are correctly configured for all sending IPs and domains.
Common pitfalls
Assuming authentication is handled automatically by the ESP without verification.
Failing to set up DKIM for all email sending platforms and subdomains.
Using a 'from' domain that does not align with your SPF or DKIM records.
Expert tips
Regularly check your email headers to confirm SPF, DKIM, and DMARC passes for all variations of your 'from' addresses.
Educate all teams sending email on behalf of your domain about the importance of consistent branding and authentication.
Use a DMARC reporting tool to gain visibility into your email ecosystem and identify authentication gaps.
Expert view
Expert from Email Geeks says checking authentication settings is crucial when sending with an alternate domain. If it does not authenticate fully, it could indeed appear as spoofing and lead to deliverability issues.
2023-02-08 - Email Geeks
Expert view
Expert from Email Geeks says that while the 'mailed-by' (Return-Path/SPF) domain being different from the 'from' domain is often acceptable, it is generally best for the DKIM signed-by domain to precisely match the 'from' domain whenever possible for optimal deliverability.
Google and 
Microsoft, strictly check for SPF and DKIM alignment, alongside a strong DMARC policy. If SPF fails or if the DKIM signature doesn't match the "from" domain, the email's legitimacy comes into question.
