Definition
Email sending domain strategy involves segmenting email traffic across multiple subdomains so that each email type develops its own independent reputation. Marketing emails sent from mail.example.com, transactional emails from transactions.example.com, and newsletters from newsletters.example.com each build separate sending histories. If marketing emails trigger spam complaints, the transactional sending domain remains unaffected, keeping password resets and order confirmations in the inbox.
Benefits
- Isolates reputation damage to the affected subdomain rather than the entire sending programme
- Enables different authentication policies per email type (e.g. stricter DMARC on transactional domains)
- Provides cleaner data for deliverability monitoring per email category
- Simplifies ISP feedback loop management by separating complaint data by subdomain
Best Practices
- Use a minimum of three subdomains: marketing, transactional, and internal or operational
- Warm each subdomain independently with gradual volume increases
- Monitor reputation per subdomain separately and set distinct alert thresholds
- Ensure all sending domains have correct SPF, DKIM, and DMARC records configured
Related Glossary Terms
BIMI
BIMI (Brand Indicators for Message Identification) is an email standard that allows brands to display their logo next to their emails in supported email clients. It requires DMARC enforcement at quarantine or reject policy.
Bounce Classification
Bounce classification uses SMTP codes (550, 551, 552, 553, 554, 450, 451, 452) and enhanced status codes to categorise permanent and transient delivery failures.
DKIM (DomainKeys Identified Mail)
DKIM (DomainKeys Identified Mail) is an email authentication method that uses digital signatures to verify that an email was not tampered with during transit and comes from a authorised domain.
DMARC Alignment
DMARC identifier alignment determines whether the domain in the From header matches the domains used in SPF and DKIM authentication. Strict or relaxed.
DMARC (Domain-based Message Authentication)
DMARC (Domain-based Message Authentication, Reporting and Conformance) is an email authentication protocol that builds on SPF and DKIM to prevent domain spoofing and provide reporting on authentication failures.
Acceptance Rate
Acceptance rate is the percentage of emails submitted for delivery that are accepted by the recipient's mail server, representing the first deliverability checkpoint before inbox placement is determined.