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Know before you build
Email Sending Limits & Best Practices
How to keep your email arriving in inboxes instead of spam folders — starting with your very first send.
Email deliverability is a reputation score, and you start with none. Mailbox providers decide whether to trust you based on how people react to your first few thousand messages. Get that period right and inbox placement takes care of itself. Get it wrong and it takes months to recover.
📧Before your first send
- Authenticate your sending domain. Unauthenticated mail from a new sender is filtered aggressively. This is Step 3.
- Send from a real address at your own domain, not a free mailbox provider address.
- Set a reply-to address that a human actually reads.
- Confirm every contact on your list gave you permission. Purchased and scraped lists will end your sending reputation in a single campaign.
🔥Warming up a new sending domain
Don't send to ten thousand people on day one. Build volume gradually so providers see steady, well-received sending rather than a spike. Keep cold sending to roughly 200 a day while you warm up.
| Week | Send to | Focus |
|---|---|---|
| 1 | Your most engaged contacts only — recent clients, people who reply to you | Opens and replies |
| 2 | Roughly double week one | Watch bounce rate |
| 3 | Double again | Watch complaint rate |
| 4+ | Continue doubling while metrics stay healthy | Full list by week five or six |
📈The numbers that matter
| Metric | Healthy | Act now |
|---|---|---|
| Bounce rate | Under 2% | Over 5% |
| Spam complaint rate | Under 0.1% | Over 0.3% |
| Unsubscribe rate | Under 0.5% | Over 1% |
| Open rate | Varies by industry | A sharp drop means placement changed |
Your bounce rate goes over 5% or complaints go over 0.3%. Pause, clean the list, and find out what changed. Continuing to send through those numbers is how a domain gets blocked rather than filtered.
🛡️Practices that protect you
- Segment before you send. Relevant mail to a small group beats generic mail to everyone, on every metric including cost.
- Suppress the disengaged. If someone hasn't opened anything in six months, stop mailing them. They're dragging your reputation down.
- Make unsubscribing easy. A hidden unsubscribe link produces spam complaints instead, and complaints hurt far more.
- Keep a consistent from name and address. Rotating sender identities looks evasive to filters.
- Write subject lines that match the content. Misleading subject lines produce complaints on open.
- Avoid a single large image with no text. Filters can't read it, and neither can anyone with images turned off.
⚖️Required in every marketing email
- A working unsubscribe link
- A real physical mailing address for your business
- An accurate from name and subject line
These aren't preferences. They're legal requirements for commercial email in the US, and comparable requirements exist elsewhere.