The sender domain is the domain that appears after the @ in the From: address of an outbound email. For cold outreach, the standard practice is to send from a dedicated sender domain (e.g., get-acmecorp.com or try-acmecorp.com) rather than your primary corporate domain. This isolates outbound reputation risk, allowing you to scale cold sends without endangering internal mail, transactional notifications, or customer communications.
Why use a separate sender domain at all?
Reputation in email is domain-level. If you send 10,000 cold emails per month from your primary domain and a small percentage get spam-reported, your primary domain's reputation drops. That drop affects every email your company sends, including order confirmations, sales follow-ups to existing customers, and CEO emails to investors. Separating the sender domain quarantines that risk. If the outbound domain ever gets blocklisted, you spin up a new one in a week without disrupting anything else.
A typical setup uses 2-5 sender domains in rotation, each with 3-5 mailboxes. That gives you 6-25 sending identities sharing the load. No single mailbox sends more than 40-50 emails per day, which keeps reputation healthy across Gmail and Outlook.
How do you choose a good sender domain?
Three rules. First, it should be brand-adjacent so the prospect recognizes you (e.g., get-acmecorp.com if your brand is Acme Corp), but distinct enough to avoid email spoofing concerns. Second, it should be a real top-level domain (.com, .co, .io) and not look like a throwaway (.xyz, .top). Third, all the standard infrastructure has to be configured before the first send: SPF, DKIM, DMARC, a custom tracking subdomain, MX records, and a real-looking landing page on the root URL so the domain doesn't return a blank page when checked. ReachIQ Email Health manages the full sender-domain pool and rotation automatically.
Related questions
How many sender domains do I need?
It depends on volume. For under 500 sends per day, two domains is enough. For 500-2000 per day, four to six. Above 2000, you're running a pool of ten or more with active rotation and reputation monitoring. The cap is set by per-mailbox limits, not domain count.
Can I send cold email from my primary domain?
You can, but it's risky. Many teams start there and migrate to a dedicated sender domain after the first deliverability scare. The migration takes 4-8 weeks (warmup time) so most playbooks recommend setting up the dedicated domain on day one before you ever send a cold email.
Should the sender domain match my company's website domain?
No, deliberately not. A close variant works best (your brand plus a verb prefix like "get-", "try-", "hello-"). Some teams use a completely different domain ("salesteam.io"); that works for big brands but feels disconnected for smaller companies where the prospect needs to recognize you.