Email marketing remains a critical channel for Australian businesses. When using Mailchimp alongside Microsoft 365 (Office 365), many organisations face deliverability issues, DNS conflicts, and authentication failures. The solution is to create a dedicated subdomain for Mailchimp. This blog explains why this approach works, how to implement it, and how it benefits your brand’s reputation and performance.
Why Mailchimp and Office 365 conflict
Microsoft 365 manages your primary domain’s email traffic. It uses strict SPF, DKIM, and DMARC policies to protect against spoofing. Mailchimp also requires these records to be published. When both services try to authenticate from the same domain, conflicts arise. These include:
- SPF record limits being exceeded
- DKIM key collisions
- DMARC misalignment
- Deliverability drops due to failed authentication
What is a subdomain and why use one
A subdomain is a prefix added to your main domain, such as email.yourdomain.com. It allows you to isolate Mailchimp’s email traffic from your primary domain. This separation provides several benefits:
1. Improved deliverability
Mailchimp can authenticate emails using its own SPF and DKIM records without interference from Office 365. This ensures higher inbox placement and fewer bounces.
2. DNS record independence
You can publish Mailchimp’s DNS records on the subdomain without affecting your root domain’s configuration. This avoids SPF flattening and TXT record conflicts.
3. Brand consistency
Using a branded subdomain like news.yourdomain.com maintains trust with recipients while clearly identifying marketing content.
4. Easier troubleshooting
If issues arise, isolating Mailchimp traffic makes it easier to diagnose problems without impacting your core business email.
5. Compliance with best practices
Email authentication standards recommend using subdomains for third party senders. This aligns with DMARC enforcement and domain reputation management.
How to set up a subdomain for Mailchimp
Step 1: Choose your subdomain
Pick a subdomain that reflects your brand and purpose. Common choices include:
- email.yourdomain.com
- news.yourdomain.com
- marketing.yourdomain.com
Step 2: Create the subdomain in DNS
Log in to your DNS provider (Cloudflare, GoDaddy, Crazy Domains, VentraIP, DreamIT Host etc.) and create the subdomain. This may involve adding a new zone or simply publishing records under the subdomain.
Step 3: Add Mailchimp DNS records
Mailchimp will provide the exact records needed. Typically, you will add:
| Type | Name | Value | Purpose |
| CNAME | k1._domainkey.email | dkim.mcsv.net | DKIM authentication |
| TXT | v=spf1 include:servers.mcsv.net ~all | SPF alignment | |
| TXT | _dmarc.email | v=DMARC1; p=none; rua=mailto:dmarc@yourdomain.com | DMARC policy |
Replace email with your chosen subdomain prefix.
Step 4: Verify the domain in Mailchimp
In Mailchimp:
- Go to Website → Domains
- Add your subdomain
- Publish the provided DNS records
- Click Verify once propagation is complete
Step 5: Set the subdomain as your default sender
After verification, configure Mailchimp to use the subdomain for all campaigns. This ensures consistent authentication and branding.
Office 365 SMTP relay considerations
If you are relaying emails through Office 365, ensure the following:
- The MAIL FROM domain is accepted in your Microsoft 365 tenant
- You use port 25 with TLS enabled
- You create an inbound connector for your relay IP
- You add the relay IP to your SPF record if needed
This ensures that transactional emails sent via Office 365 do not conflict with Mailchimp’s marketing traffic.
DNS provider tips
Different DNS providers have different quirks:
- Cloudflare: Fast propagation, supports CNAME flattening
- GoDaddy: May strip underscores in TXT records. Use quotes to preserve formatting
- Crazy Domains: Slower propagation. Manual entry required
- AWS: Ideal for technical users. Supports advanced routing
Always test your records using MXToolbox or Google Admin Toolbox.
WordPress integration
If your website runs on WordPress, you can:
- Use Mailchimp plugins to embed signup forms
- Track campaign performance using UTM tags
- Sync WooCommerce customers with Mailchimp lists
- Add popups and landing pages using Mailchimp blocks
Ensure your WordPress site uses the same subdomain for email links to maintain domain alignment.
Conclusion
Creating a subdomain for Mailchimp when using Office 365 is a smart move for Australian businesses. It improves deliverability, protects your domain reputation, and simplifies DNS management. When paired with WordPress, it creates a seamless marketing ecosystem that supports growth and engagement.