Definition
An email sending domain is the domain used in the From: header and envelope of your email messages. It is distinct from your website domain and carries its own reputation with mailbox providers. Since Google and Yahoo updated their sender requirements in February 2024, domain alignment has become mandatory for bulk senders — meaning the domain in the From: header must match the domain authenticated by SPF and DKIM, or at least share the same organisational domain.
A subdomain strategy involves dedicating specific subdomains (e.g., marketing.yourdomain.com, transactional.yourdomain.com) to different email streams. This isolates the reputation of marketing emails from transactional ones, preventing a poorly performing campaign from damaging critical password-reset or order-confirmation emails. Most enterprise senders use at least three subdomains: marketing, transactional, and operational.
Domain reputation is separate from IP reputation. A mailbox provider evaluates both the sending IP address and the sending domain when deciding whether to deliver, quarantine, or reject a message. The domain reputation is increasingly weighted more heavily than IP reputation, particularly in Gmail's filtering algorithm. Domain age matters — a brand-new domain has no history and will be treated cautiously for the first 4-8 weeks until a positive sending pattern is established.
Best Practices
Use a separate subdomain for marketing emails to protect transactional deliverability. If your marketing subdomain suffers a spike in spam complaints, your transactional subdomain's reputation remains unaffected. Configure SPF, DKIM, and DMARC on every subdomain independently.
Align your sending domain with your From: header domain (strict DKIM alignment). This means the d= domain in the DKIM signature must match the domain in the From: address. Gmail's post-2024 requirements make this essential for bulk senders sending over 5,000 messages per day to Gmail recipients.
Warm up a new sending domain gradually over 4-6 weeks, starting with low-volume, highly engaged recipients. Send no more than a few hundred emails per day in week one, doubling volume each week while monitoring open rates, complaint rates, and bounce rates. A sudden spike in volume from a new domain triggers spam filters.
Avoid using shared root domains for bulk marketing sends. Your root domain (yourdomain.com) should be reserved for transactional email or personal correspondence. Bulk marketing sends on the root domain risk contaminating the domain's overall reputation, potentially affecting main website email deliverability.
Monitor domain reputation using Google Postmaster Tools and Yahoo Sender Hub. Check spam complaint rates, domain reputation (bad/neutral/good), and authentication pass rates weekly. Any complaint rate above 0.1% indicates a domain health issue that requires investigation.
Frequently Asked Questions
Frequently Asked Questions
No, a subdomain does not automatically improve deliverability. It provides reputation isolation, so problems in one stream do not spread to others. Each subdomain builds its own reputation from zero and must be warmed up independently.
Typically 4-8 weeks of consistent, positive sending behaviour. Factors include sending volume, engagement rates, complaint rates, and domain age. Older domains with positive history build reputation faster than brand-new domains.
Domain alignment ensures the domain in your `From:` header matches the domain authenticated by SPF or DKIM. Gmail and Yahoo now require it for bulk senders. Without alignment, authenticated messages can still be rejected or marked as spam.
Use marketing.yourdomain.com. This isolates newsletter reputation from your primary domain. If your newsletter receives spam complaints, your main domain and transactional emails remain unaffected. This is considered industry standard practice.
Yes, but switching domains resets your reputation to zero. Introduce the new domain gradually alongside the existing one using a subdomain strategy, and warm it up over 4-6 weeks before migrating volume. Running both in parallel for a period ensures continuity.