How does Google Workspace manage outbound authentication with multiple domains?
Michael Ko
Co-founder & CEO, Suped
Published 30 May 2025
Updated 16 Aug 2025
7 min read
When managing email for a business, especially one with multiple brands or departments, it's common to operate with multiple domains within a single Google Workspace account. While this offers flexibility, it also introduces complexities for outbound email authentication. Ensuring that emails sent from each domain are properly authenticated is critical for deliverability and maintaining sender reputation.
Many organizations face challenges with DMARC failures or emails landing in spam folders because of authentication issues when using multiple domains. This is often due to misunderstandings about how Google Workspace handles authentication, particularly SPF and DKIM, for different domain setups. I'll outline how outbound authentication works and provide strategies to help you navigate these complexities, ensuring your emails reach their intended recipients.
Google Workspace supports several ways to manage multiple domains, each with different implications for outbound authentication. Understanding these setups is the first step to ensuring proper deliverability.
A primary domain is the main domain you set up when you create your Google Workspace account. All users are associated with this domain by default. Secondary domains, also known as additional domains, are separate domains added to your Google Workspace account. Users can be assigned email addresses on these secondary domains, and these domains operate largely independently with their own set of DNS records for authentication, including SPF and DKIM. This is generally the preferred method for managing distinct brands or departments with their own sending identities.
Then there are domain aliases. A domain alias allows users on your primary domain to receive emails sent to an address on the alias domain. For instance, if your primary domain is yourcompany.com and you add yourbrand.com as an alias, an email to info@yourbrand.com will go to info@yourcompany.com. The critical difference is that emails sent from an alias domain will typically authenticate against the primary domain's settings, which can lead to DMARC alignment issues.
Domain type
Purpose
Outbound authentication
Primary domain
Main domain for your Google Workspace account and user identities.
Authenticates using its own SPF and DKIM records.
Secondary domain
Separate domains under the same account, allowing distinct user identities.
Configured with its own SPF and DKIM, ensuring proper alignment.
Domain alias
Allows users on primary domain to receive mail at a different domain.
Typically authenticates against the primary domain's settings, causing DMARC issues.
Outbound authentication mechanisms in Google Workspace
For outbound email from Google Workspace, the fundamental authentication protocols—SPF, DKIM, and DMARC—are always at play. Google Workspace manages these for all domains provisioned within your account.
The Sender Policy Framework (SPF) for Google Workspace generally involves adding their servers to your domain's SPF record. This single SPF record typically covers all domains under your Google Workspace account, as all outgoing mail flows through Google's infrastructure. However, if you use a third-party email service provider (ESP) alongside Google Workspace for some domains, you'll need to ensure your SPF record includes all legitimate sending sources.
The DomainKeys Identified Mail (DKIM) signature is critical. For each primary and secondary domain, you'll generate a unique DKIM key within the Google Workspace Admin console and publish it as a TXT record in your DNS. This signature authenticates the sending domain. The challenge with multiple domains, especially aliases, is ensuring the d=domain (signing domain) in the DKIM signature aligns with the From address visible to the recipient. For secondary domains, this is straightforward, as Google generates a DKIM key for that specific domain. However, for alias domains, mail might be signed by the primary domain's DKIM, leading to DMARC failures if not handled correctly.
DKIM record example for Google WorkspaceDNS
v=DKIM1; k=rsa; p=MIIBIjANBgkqhkiG9w0BAQEFAAOCAQ8AMIIBCgKCAQEAs...[YOUR PUBLIC KEY HERE]...IDAQAB
Finally, DMARC (Domain-based Message Authentication, Reporting, and Conformance) relies on both SPF and DKIM to pass authentication and alignment. For a message to pass DMARC, at least one of these mechanisms must align with the From domain. Google Workspace's handling of DMARC is robust, but it requires careful configuration, especially when using domain aliases or third-party senders. If your email is sent from an alias, and DKIM is signed by the primary domain, it will fail DMARC alignment unless you have a lax DMARC policy or specific routing rules in place.
Even with proper setup, you might encounter issues. One common problem is DMARC failing due to a DKIM signing domain mismatch. This often happens when users configure their Gmail to send as an address on another domain (an alias or a user from another domain) without proper backend configuration.
If a user on your primary domain user@primary.com configures their Gmail to send mail asuser@alias.com, the outgoing email might still be DKIM-signed by primary.com, causing a DMARC failure for the alias.com domain. This scenario is particularly prevalent with sales outreach teams trying to send from specific branding domains.
Alias domain challenges
Emails sent from a domain alias might fail DMARC because the d=domain in the DKIM signature doesn't align with the From header (RFC5322.From). This is a common pitfall. The solution usually involves upgrading the alias to a secondary domain if distinct authentication is needed.
Tips for resolution
Review DMARC reports: These reports will clearly indicate DKIM alignment failures, pointing you to the problematic sending patterns. This is key for troubleshooting DMARC issues.
Check DKIM records: Confirm that DKIM is enabled and properly configured for all primary and secondary domains. Google Workspace provides the specific TXT records you need to publish.
Another scenario is when a Google Workspace account uses an older, possibly free, legacy edition. These older setups can sometimes exhibit wobbly authentication behavior, making it harder to ensure consistent DMARC compliance. In such cases, upgrading to a current Google Workspace subscription might resolve underlying technical issues related to email authentication. This is crucial for maintaining a healthy sender reputation and avoiding blocklist issues (or blacklist issues).
Best practices for multi-domain authentication
To ensure reliable email deliverability from your multiple domains in Google Workspace, adhering to best practices is essential. Proper configuration prevents authentication failures and helps maintain a strong sender reputation.
Problem: domain aliases for distinct sending
Using domain aliases for sending emails when you need separate authentication and reporting for each brand.
Reputation implications
A negative reputation on one alias could impact the primary domain, as outbound emails often authenticate against the primary domain's DKIM and SPF.
Solution: use secondary domains
For each distinct brand or department requiring its own outbound identity, add it as a secondary domain in Google Workspace. This allows for dedicated authentication records.
Benefits for reputation and deliverability
Independent DKIM: Each secondary domain can have its own DKIM key, ensuring that the DKIM signing domain aligns with the email's From address for DMARC pass.
Isolating reputation: A poor sending reputation on one secondary domain is less likely to affect other domains in your account, unlike with aliases. For more on this, consider how reputation affects multiple domains.
Always ensure you have SPF, DKIM, and DMARC records properly configured for every domain you send from via Google Workspace, including secondary domains. Regularly monitor your DMARC reports to identify any authentication failures or inconsistencies, as they can quickly lead to emails being marked as spam or blocked outright.
Also, if you're using third-party email service providers (ESPs) in conjunction with Google Workspace, make sure your authentication records accommodate all sending sources. This might involve including the ESP's SPF record in your domain's SPF and configuring DKIM for both Google Workspace and the ESP, if applicable.
Ensuring proper email authentication
Effectively managing outbound email authentication for multiple domains in Google Workspace is crucial for maintaining email deliverability and protecting your sender reputation. The key lies in understanding the distinction between primary, secondary, and alias domains and ensuring each has the correct SPF, DKIM, and DMARC configurations.
Prioritizing secondary domains over aliases for distinct sending identities, meticulously configuring your DNS records, and continuously monitoring your DMARC reports will help you navigate these complexities. This proactive approach ensures your emails are consistently authenticated, landing in the inbox rather than the spam folder.
Views from the trenches
Best practices
Always add distinct sending domains as secondary domains in Google Workspace, not aliases.
Verify that each secondary domain has its own unique DKIM record generated and published via Google Workspace.
Regularly check your DMARC reports to spot any authentication failures or alignment issues.
If using third-party ESPs, ensure their sending IPs and domains are also included in your SPF record and properly DKIM-signed.
Maintain separate Google Workspace accounts if you need completely isolated administrative settings or billing for different domains.
Common pitfalls
Using domain aliases for outbound email, leading to DMARC alignment failures due to primary domain DKIM signing.
Not generating and publishing unique DKIM keys for all secondary domains added to Google Workspace.
Overlooking SPF record updates when adding new sending sources or third-party ESPs.
Ignoring DMARC reports, which can hide critical authentication problems affecting deliverability.
Attempting to manage multiple, disparate businesses under one Google Workspace account with complex routing rules.
Expert tips
For optimal DMARC alignment, ensure that your 'From' address domain matches the DKIM signing domain for all outbound mail.
Consider a phased rollout when implementing DMARC policies for new domains, starting with p=none to monitor impact.
Educate users on how 'Send mail as' functionality impacts authentication, especially with alias domains.
If facing persistent DKIM signing issues, Google Workspace support might be necessary, as issues can be platform-side.
Using Google Postmaster Tools provides valuable insight into domain reputation and email deliverability performance.
Expert view
Expert from Email Geeks says the only time they have seen DKIM signing domain mismatch with independently set up domains (not aliases) is when a user configures an address from a second domain as an alias or send-as address within their primary Gmail account.
July 28, 2021 - Email Geeks
Expert view
Expert from Email Geeks says if a second domain is set up as an alias, it can have its own DKIM signing domain, but the MailFrom (RFC5321.From) domain will be that of the main domain, potentially causing DMARC alignment issues.
Google Workspace is crucial for maintaining email deliverability and protecting your sender reputation. The key lies in understanding the distinction between primary, secondary, and alias domains and ensuring each has the correct SPF, DKIM, and DMARC configurations.
