Cold email deliverability is the answer to one question: does your email actually reach the inbox, or does the mailbox file it as spam? It lands in spam when the receiving server can't prove the message is really from your domain, or when it sees signals of bulk sending — a dirty list, sudden volume, spam complaints, bounced addresses. The fix has three parts: authenticate your domain (SPF, DKIM, DMARC), protect your sending reputation, and send like a person at a sane pace. You can write the perfect cold email, and none of it matters if it never reaches the person. This page is the plain-English setup checklist a BDR uses before scaling outreach.
Why your email lands in spam
Mailboxes decide your fate in milliseconds on three things:
- Authentication — can they prove it's you? Three records prove your domain owns the sending: SPF says which servers are allowed to send for you, DKIM cryptographically signs the message, and DMARC tells receivers what to do when the other two fail. Set all three, and your mail stops looking like a spoof.
- Reputation — do they trust your domain? New domains start with no reputation. Complaints, hard bounces, and spam-trap hits push it down; steady, wanted mail pushes it up.
- Behavior — do you look like a bulk sender? One person sending 60 short, varied emails looks human. A domain firing 500 identical emails at bought addresses looks like a bot.
The setup checklist — here is the asset
Run a new sending domain through this before you turn up volume:
- [ ] Publish SPF. A TXT record listing the servers allowed to send for your domain (e.g. your ESP). Only include servers you actually use.
- [ ] Publish DKIM. A signature key that mailboxes can verify, so they know the message wasn't altered and came from you.
- [ ] Publish DMARC. A policy that says what to do with mail that fails SPF or DKIM — start by monitoring, then move to a reject policy once real mail authenticates.
- [ ] Verify alignment. Send a test and confirm SPF and DKIM pass and align to your root domain — most cold-email problems are misaligned subdomains.
- [ ] Warm up the domain. Ramp volume over a few weeks from a handful of sends a day, not hundreds on day one. Warm-up is a reputation build, not a magic bullet.
- [ ] Send from a real, human account. A custom domain and a real sender beat a free webmail address every time.
- [ ] Use a clean, confirmed list. Build your prospect list from research, not bought or scraped data, and remove hard bounces promptly.
- [ ] Keep an eye on complaints and bounces. If either climbs, slow down, clean the list, and fix the subject lines and copy that read as spam.
- [ ] Make opting out easy. A working unsubscribe is a legal requirement and a reputation signal — recipients who can leave don't need to hit "report spam."
What warm-up actually is (and isn't)
"Email warm-up" sounds like a button, but it's a reputation build: you send small, increasing, genuinely-opened mail so mailboxes learn your domain is real and wanted. It does not rescue a dirty list or make spam-shaped mail deliver. The honest version is: authenticate properly, send to a clean list of researched contacts, keep volume steady, and let weeks of consistent behavior build trust. Every spam-filter trick you skip in favor of that is a reputation debt you'll pay in the inbox placement rate.
Next: the email that's worth delivering
Deliverability gets you the open; the message earns the reply. Once your mail is landing, make it worth reading with the cold email template and the subject lines that earn opens, then scale it into a proper follow-up sequence.