What "deliverability" means
Deliverability is whether your email reaches the inbox, lands in spam, or doesn't arrive at all. Email providers decide this using your domain's reputation, technical authentication, how recipients react to your emails and the content itself. Cold email is judged especially strictly, because recipients didn't ask to hear from you.
Before anything else: follow the law where your recipients are. Rules differ between countries, for example the CAN-SPAM Act in the US and GDPR and PECR in the UK and EU. Always identify yourself, give an easy way to opt out and honour it promptly.
1. Set up your domain properly
Three DNS records tell email providers that your emails are really from you:
- SPF lists the servers allowed to send email for your domain.
- DKIM adds a digital signature that proves the email wasn't changed on the way.
- DMARC tells providers what to do with emails that fail those checks, and sends you reports.
Many teams send cold email from a separate domain similar to their main one, so any reputation problems don't affect everyday company email. Give that domain a real website and a real person behind each mailbox.
2. Warm up new mailboxes
A brand-new mailbox that suddenly sends hundreds of emails looks suspicious. Start small and increase gradually over several weeks, for example a handful of emails a day in the first week, rising week by week. Our own system uses a stepped warm-up per mailbox and never lets a single mailbox exceed a daily cap.
3. Send like a person, not a machine
- Space emails out with natural, varied gaps of a few minutes, not bursts.
- Keep daily volume per mailbox modest; spread larger campaigns across several mailboxes.
- Send during sensible hours for the recipient's time zone.
- Send follow-ups as replies in the same thread, from the same mailbox.
4. Clean your list before you send
Bounces damage your reputation quickly. Before sending, remove obviously invalid addresses, duplicates and role addresses that rarely belong to a decision-maker, and check that each domain can receive email. Keep a permanent do-not-contact list and check it before every send.
5. Watch bounces and pause early
Track your bounce rate per mailbox. If it rises above a few percent, stop and investigate: your list may be outdated or your data source poor. Distinguish between permanent bounces (address doesn't exist: never email again) and temporary ones (mailbox full or server busy: try later). Pausing a mailbox automatically when bounces spike is one of the best protections you can build.
6. Stop the moment someone replies
Nothing annoys people more than a "just following up" email after they've already replied, or after they asked you to stop. Read replies, opt-outs and bounces before every send, and stop the sequence for that person (and ideally their colleagues) immediately. Count only what the person actually wrote, not the quoted history or your own signature, when deciding whether someone opted out.
7. Write emails that look personal
- Keep it short, plain and relevant to the recipient's business.
- Personalise the first line with something genuinely specific, not just their first name.
- Avoid heavy images, attachments, lots of links and spammy phrases.
- Make one clear, low-effort ask, like a quick reply.
- Test subject lines one change at a time, and give each version enough sends before judging.
8. Be careful with tracking
Open tracking relies on hidden images and is increasingly unreliable. Link-click tracking is more useful, but be aware that email security scanners often click links automatically. Filter out clicks that happen within seconds of sending or come from known scanners, or you'll chase false signals.
9. Build in safety
If your sending system crashes mid-send, it should never email the same person twice. A good system re-checks each lead right before sending and holds anything uncertain for a human to check. These details sound small, but they're the difference between a trusted sender and a blocked one.
A quick deliverability checklist
- SPF, DKIM and DMARC set up
- Separate sending domain with a real website
- Gradual warm-up and daily caps per mailbox
- Clean list and do-not-contact list
- Automatic pause on high bounces
- Sequences stop on reply or opt-out
- Short, personal, plain emails
We built these rules into our own Outreach Engine. If you'd like a system like it for your business, see our automation service.