To improve email deliverability, authenticate your domain with SPF, DKIM and DMARC, warm up new inboxes, send only to verified addresses, stay under daily sending limits, write plain emails with an easy unsubscribe, and keep your spam rate under 0.10% in Google Postmaster Tools.
Deliverability is whether your email reaches the inbox, not just the server. An email can be delivered and still land in spam, and the fixes for that are mostly in your DNS, your list and your sending habits.
The twelve fixes below are in the order to do them. Rules from Gmail, Yahoo and Microsoft are taken from their own help pages, so you know what is required and what is advice.
Paste a cold email and get a score out of 100, with the words and links to change. No sign-up.
Check your email for spam wordsFree, runs in your browser| Fix | What to do | Area |
|---|---|---|
| 1. Publish an SPF record | List every service that sends for your domain | Authenticate |
| 2. Turn on DKIM | Sign mail with a 2048-bit key where you can | Authenticate |
| 3. Publish a DMARC record | Start at p=none with reports, aligned to your From domain | Authenticate |
| 4. Warm up new inboxes | Start low and raise volume slowly, with no spikes | Warm up |
| 5. Verify addresses before you send | Remove invalid and risky addresses | List |
| 6. Remove bounces and non-openers | Stop mailing people who never engage | List |
| 7. Stay under daily limits | Spread volume across inboxes and domains | Limits |
| 8. Send at a steady rate | Back off when you see deferrals or 4xx errors | Limits |
| 9. Write plain, honest emails | No fake Re:, hidden text or link shorteners | Content |
| 10. Make unsubscribing easy | One-click unsubscribe for bulk mail | Content |
| 11. Watch your spam rate | Keep it under 0.10% in Postmaster Tools | Monitor |
| 12. Fix problems in order | Authentication first, then volume, then content | Monitor |
Fixes 1 to 3 are required by Gmail, Yahoo and Outlook for bulk senders. Fixes 4 to 12 decide where your mail lands once it is accepted.
Authenticate: SPF, DKIM, DMARC
Authentication proves your email really comes from your domain. Gmail requires SPF or DKIM from every sender, and SPF, DKIM and DMARC from senders of 5,000 or more messages a day to Gmail accounts.
Yahoo sets the same rules for bulk senders, and Microsoft says Outlook requires SPF, DKIM and DMARC from domains that send more than 5,000 emails a day. Set all three up even if you send less: it costs nothing.
1. Publish an SPF record
SPF is a DNS record that lists the servers allowed to send for your domain. Gmail's guidelines say your SPF record should include every service that sends for you, or their messages are more likely to be marked as spam.
2. Turn on DKIM
DKIM adds a signature that lets the receiver check the domain owner sent the message. Gmail requires a key of at least 1024 bits and recommends 2048 bits if your provider supports it.
3. Publish a DMARC record
DMARC tells receivers what to do when SPF or DKIM fails. To pass, the authenticated domain must match the domain in your From: address. Yahoo asks bulk senders for a policy of at least p=none.
Add a rua tag so you get DMARC reports. Yahoo strongly recommends it during setup, and Google recommends reports to spot anyone sending as your domain.
Warm up new inboxes
A new inbox or domain has no sending history, so providers watch it closely. Google advises starting with a low volume to engaged recipients and raising it slowly over time.
4. Ramp volume slowly, with no spikes
Google warns that suddenly doubling your volume can lead to rate limits or a drop in reputation. Daily sending lets you ramp faster than weekly sending, and so does good recipient feedback.
Warmup tools automate this by sending and replying between real inboxes. We compare them in our guide to the best email warmup tools.
Clean your list
Every bounce and every ignored email tells providers your mail is unwanted. List hygiene is the cheapest deliverability fix there is.
5. Verify addresses before you send
Run new lists through an email verifier and drop invalid and risky addresses. Yahoo tells senders to monitor hard and soft bounces and remove invalid recipients promptly.
6. Remove bounces and people who never engage
Google suggests unsubscribing recipients who do not open or read your messages, and automatically unsubscribing addresses with several bounces. Never buy lists: both Google and Yahoo tell senders not to.
Sending limits
Each mailbox has a daily cap, and going near it is a red flag even before you hit it. Cold email teams spread volume across many inboxes and domains for this reason.
7. Stay under daily limits
Google Workspace allows 2,000 messages a day per user, and 500 on trial accounts. Microsoft's Exchange Online has a recipient rate limit of 10,000 recipients a day per mailbox. Cold email inboxes are usually run far below these caps.
8. Send at a steady rate
Google asks bulk senders to send at a consistent rate and avoid bursts. When Gmail rejects mail with error 4.7.28, it says to stop for at least 10 minutes, then restart from a single connection.
Content and spam words
Content matters less than authentication and list quality, but it is the part you change most often. Gmail's guidelines focus on deception: misleading subjects, hidden content and unclear links.
9. Write plain, honest emails
Gmail asks senders not to start subject lines with Re: or Fwd: unless the email is a real reply or forward, not to hide content with HTML or CSS, and to keep links visible and easy to understand.
For cold email, keep the first message to one link or none, skip link shorteners and fill every merge tag. Our free spam checker flags each of these and scores the email out of 100.
Check your email for spam words before your next campaign goes out.
10. Make unsubscribing easy
Senders of more than 5,000 messages a day to Gmail must support one-click unsubscribe on marketing and subscribed messages. Yahoo asks bulk senders to honor unsubscribes within 2 days.
For cold email, a plain opt-out line such as "reply no and I will not email again" gives people an option other than the spam button.
Monitor and fix
You cannot see where your email lands from your own Sent folder. Use the provider tools, and check them weekly while you are scaling up.
11. Watch your spam rate
Google says to keep the spam rate in Postmaster Tools below 0.10% and never reach 0.30%. Yahoo asks bulk senders to stay below 0.3%, and its Complaint Feedback Loop sends you copies of spam reports.
12. Fix problems in the right order
When inbox placement drops, check authentication first, then bounces and complaints, then volume, and only then the copy. Microsoft rejects non-compliant mail from high-volume domains with error 550 5.7.515.
Once the email lands, the next job is answering the replies fast. For cold email teams running many inboxes across sequencers, we recommend Revbound, our product. It puts every sequencer reply in one inbox, drafts answers with free calendar times and books the meeting when the lead accepts.
Answers go out from the same mailbox the lead wrote to, and Revbound does not send cold email, so your sequencer keeps sending. Still choosing a sender? See the best cold email software.
Email deliverability checklist
Run through this list for every new domain, and again whenever open or reply rates drop.
- SPF lists every service that sends for the domain.
- DKIM is on, with a 2048-bit key where supported.
- DMARC is published at p=none or stricter, with reports.
- New inboxes ramp up slowly, with no sudden spikes.
- Every list is verified before the first send.
- Hard bounces and repeat non-openers are removed.
- Each inbox stays well under its daily limit.
- No fake Re: subjects, hidden text or link shorteners.
- Bulk mail has one-click unsubscribe.
- Spam rate stays under 0.10% in Postmaster Tools.
FAQ
How do I improve email deliverability?
Authenticate your domain with SPF, DKIM and DMARC, warm up new inboxes, verify your list and remove bounces, stay under daily sending limits, write plain emails with an easy unsubscribe, and keep your spam rate under 0.10% in Google Postmaster Tools.
How do I improve email deliverability and avoid spam?
Send only to people who expect your email, and make it easy to opt out. Avoid fake Re: or Fwd: subject lines, hidden text and shortened links, and keep links to one or none in a first cold email. Then check your copy with a spam word checker before you send.
What causes email deliverability issues?
The usual causes are missing or broken SPF, DKIM or DMARC records, sending too much too soon from a new inbox, high bounce rates from an unverified list, spam complaints, and misleading subject lines or hidden content.
How do I improve my email delivery rate?
Delivery rate drops when mail bounces or is rejected. Verify addresses before you send, remove hard bounces at once, fix authentication so providers do not reject you, and slow down when you see deferral errors such as Gmail's 4.7.28.
How do I improve email deliverability in HubSpot?
Connect your email sending domain in HubSpot. HubSpot's help page says this sets up MX, DKIM, SPF and DMARC records so its marketing emails meet the standards inbox providers enforce. The list and content fixes in this guide still apply.
Does warming up an inbox improve deliverability?
Yes, for new inboxes and domains. Google advises starting with a low volume to engaged recipients and raising it slowly, because sudden spikes can lead to rate limits or a drop in reputation. Warmup tools automate that ramp.
Related reading
- ComparisonThe best email warmup tools
- Free toolFree email spam checker for cold email
- ComparisonThe best cold email software
