Sending Domain and Subdomain Strategy

Where you send from shapes how inbox providers judge your mail. A marketing campaign that draws complaints should not put your password resets at risk. Separating mail streams across subdomains is how senders contain that risk.

Why Separate Mail Streams

Inbox providers track reputation per domain. If marketing and transactional mail share a domain, they share a reputation. One bad campaign, a stale segment, or a complaint spike from a promotion can push order confirmations and password resets toward spam.

Separating streams gives each one its own reputation. Marketing problems stay contained to the marketing subdomain. Transactional mail, which usually has excellent engagement, keeps its strong record.

The trade-off is that each domain builds reputation independently. Two domains means two warmups and two reputations to maintain.

Typical Setups

Stream	Common domains	Notes
Marketing	mail.example.com, news.example.com	Higher volume, higher complaint risk
Transactional	tx.example.com, or the root example.com	Expected mail, strong engagement
Required notices	A separate established subdomain	See Mandated Emails

The pattern is consistent: keep the riskiest stream on its own subdomain, and keep transactional mail on the cleanest one. Some teams put transactional on the root domain because corporate mail already sends from it and the reputation is established.

Subdomains, Not Lookalike Domains

Use subdomains of your real domain. Do not register lookalike or cousin domains like example-mail.com or getexample.net for sending.

Lookalike domains have problems:

• They start with zero reputation and no connection to your established domain.
• They look like phishing. Attackers register cousin domains to impersonate brands, and filters know it.
• Recipients do not recognize them, which raises complaints.
• You now maintain DNS, DMARC, and renewal for an extra domain forever.

A subdomain inherits recognition from your brand and ties your sending history to the domain customers already trust.

How Subdomain Reputation Works

At Gmail, subdomains build their own reputation but are also connected to the organizational (root) domain. A new subdomain of an established domain starts warmer than a brand-new domain, because Gmail sees the relationship. But severe problems flow upward. Sustained abuse on a subdomain can drag down how Gmail views the whole organizational domain.

Treat subdomains as containment, not immunity. They limit how far a marketing problem spreads. They do not let you burn one subdomain and walk away clean.

Each new subdomain still needs its own warmup. Inherited trust shortens the ramp. It does not remove it.

When One Domain Is Fine

Stay on a single sending domain when:

• You send modest, consistent volume.
• Your list is opt-in and regularly cleaned. See List Hygiene.
• Complaint and bounce rates are healthy.
• You have one brand and one audience.

A single well-run domain beats a fleet of half-maintained subdomains. Splitting adds setup, warmup, and monitoring work, so only take it on when the risk justifies it.

When to Split

Split streams onto separate subdomains when:

• Marketing volume is high relative to transactional volume.
• You send to risky segments, like re-engagement lists or older imports.
• You run multiple brands with different audiences.
• You need to send a mandated blast to a list that includes cold contacts. See Mandated Emails.
• Transactional mail is business-critical and you cannot afford collateral damage.

Decision Table

Your situation	Recommended setup
Small sender, clean opt-in list, consistent volume	One domain for everything
Growing marketing volume, transactional mail matters	Marketing on mail.example.com, transactional on root or tx.example.com
Multiple brands	One subdomain or Site per brand
Re-engagement or risky segments	Risky sends on a dedicated marketing subdomain
One-time mandated blast	Separate Site and established subdomain, per Mandated Emails
Damaged reputation	Fix list quality first, do not domain-hop

How This Works in Bento

Sites are how Bento separates sending streams. Each Site has its own sending domain, its own DNS setup, and its own suppression list. To split marketing and transactional mail:

1. Create a Site for each stream. See Account Structure and Sites.
2. Assign each Site its sending domain, for example mail.example.com for marketing and tx.example.com for transactional.
3. Complete DNS Setup for each domain. Each one needs its own verified records.
4. Warm each new subdomain following the Domain Warmup Guide, starting with the most engaged recipients.
5. Watch each stream separately in the Deliverability Monitor and in Google Postmaster Tools.

Keep the From address on each stream consistent once it is established. Recipients learn to recognize the sender, and switching domains resets that trust along with the reputation.