Email campaign deliverability: the 4 steps to fix before sending

Part of our guide on why isnt my tech working after update

Most campaigns fail inbox for three DNS lines, not bad copy — fix them in order and watch placement jump.

What you need before you fix deliverability

You need three DNS records live before any tool can help your inbox rate. Without them your mail looks forged and providers drop it.

Say you run a small shop on Gmail or Outlook with your own domain. Picture sending 500 newsletters that mostly land in spam. The cause is usually missing authentication, not bad copy.

Gather access to your DNS panel, your sending domain, and a test inbox on Gmail and Outlook. You will also need a way to check SPF, DKIM and DMARC and to scan your list for bad addresses.

This order matters. Technical checks first, then list cleaning, then content, then sending habits. Skip the order and you chase symptoms. There is more on tests to distinguish router delay in a separate guide.

• Access to DNS for your sending domain – to add or edit TXT and CNAME records
• An inbox tester or free DMARC checker – to verify SPF, DKIM and DMARC pass
• Your current list exported as CSV – to scan for invalid, role and catch-all addresses
• A second test address on Gmail and Outlook – to see spam vs inbox placement

How to improve email deliverability for campaigns starts with authentication

A missing SPF record fails about 1 in 4 small business sends on the first check, depending on host. Providers treat that as spoof risk and filter you hard.

Say you just connected a new campaign tool and sent a test. Picture Gmail showing "mailed-by" as your host, not your domain. That mismatch means SPF or DKIM did not align.

Start with SPF. It lists which servers may send for your domain in a TXT record. Keep it under 10 lookups and include only your real senders, or it breaks and fails. Next add DKIM. It signs each message with a key published as a CNAME or TXT record, usually 1024-bit or 2048-bit depending on provider. End with DMARC. It tells receivers what to do if SPF or DKIM fails and where to send reports, start at p=none then move to p=quarantine. For the detail, see our notes on monitor spam traps and reputation.

Think of authentication like a photo ID at the door. SPF says where you are allowed to send from, DKIM proves the envelope was not opened, and DMARC is the instruction you leave for the bouncer. If any piece is missing, you wait outside.

1. Find your current SPF: look up TXT at your domain and confirm it includes your campaign provider and your host.
2. Publish DKIM: copy the two CNAME or TXT values from your provider into DNS and wait 30-60 minutes for propagation.
3. Create DMARC: add TXT at _dmarc.yourdomain.com with v=DMARC1; p=none; rua=mailto:you@yourdomain.com
4. Send a test to Gmail, open Show original, and confirm SPF pass, DKIM pass and DMARC pass all show green.

How to check and clean email lists to reduce bounces

A list with 2% hard bounces on a 5,000 contact send triggers throttling at major providers, sooner if you hit spam traps. That rate depends on age of the list and source, older scraped lists bounce more.

Say you imported 2,000 addresses from an old form and a spreadsheet. Picture 80 bouncing as "user unknown" and one spam trap firing. Your next campaign lands in spam for everyone. There is more on nas drive inaccessible after outage in a separate guide.

You need to know three buckets: invalid, risky and catch-all. Invalid addresses will hard bounce every time. Risky includes role accounts like info@ and known spam traps. Catch-all domains accept anything, so some mail vanishes without a bounce and hurts engagement.

ZeroBounce handles this bulk check in one pass. It validates each address in real time with 99.6% accuracy, flags invalid and risky contacts, and scores catch-all addresses so you can keep or drop them. It does not fix bad collection or replace double opt-in, and very small lists with few sends may not need a paid tool. You can run the same check manually for tiny lists by sending in small batches and removing hard bounces by hand, but that risks reputation while you learn.

1. Export your list and keep the original CSV untouched as backup.
2. Run validation to label invalid, catch-all, role and spam-trap risk. Remove invalid and high-risk before sending.
3. Re-confirm catch-all and role addresses only if you have recent engagement, otherwise archive them.
4. Re-check any list older than 60-90 days or built from mixed sources before the next large send.

How to improve email content to avoid spam filters

Filters block content that looks like mass bait even when authentication passes, often at 0.1% complaint rate thresholds that vary by provider. Engagement and content signals stack, so poor content plus low opens pushes you to spam. If that sounds like your situation, read up on difference between oem and retail license next.

Say you wrote a promo with ALL CAPS subject, four exclamation marks and three link shorteners. Picture it hitting Gmail Promotions at best, spam at worst, even to engaged readers.

Build the message for a human first, then strip spam cues. Use one clear subject under 50 characters, one main call to action, and plain links to your own domain. Keep image to text ratio near 40/60, host images on your domain, and avoid URL shorteners that hide the destination. Include a physical address and a one-click unsubscribe that works in one click.

Test before you scale. Send to seed inboxes, check placement, then send to your most engaged 25% first. If that segment opens and replies, providers trust the rest of the batch more.

• Subject line: specific, under 50 characters, no all caps or repeated punctuation
• Links: 1-3, full URLs on your domain, no shorteners, no raw IP links
• Images: compressed, with alt text, not one giant image with no text
• Footer: mailing address, list name, and List-Unsubscribe header via your tool

Which sending practices affect reputation and deliverability

A new domain or IP that jumps from 0 to 10,000 mails in a day looks like a snowshoe spam blast, and throttling can last 7-14 days depending on volume and complaints. Reputation builds on consistency.

Say you send monthly, then blast 8,000 after a break. Picture half deferred with 4xx temp blocks and the rest in spam. The gap, not the copy, caused it.

Warm steadily. Start with engaged contacts, send daily or twice weekly, and raise volume by 25-50% per day if bounces stay low and complaints near zero. Keep from and reply-to on the same authenticated domain and do not rotate domains to dodge blocks. Monitor blacklists weekly and fix the cause, not just delist, or you relist quickly. A useful rule of thumb: keep hard bounces under 2% and complaints under 0.1%, or pause and clean before the next send.

Track engagement and prune. Remove non-openers after 60-90 days of no clicks, or move them to a re-engagement flow. Providers rank recent opens and replies far above total list size.

1. Pick one sending domain and one from address and stick with it for 30 days.
2. Segment out engaged contacts from last 30-60 days and mail them first.
3. Increase daily volume 25-50% only while bounces and complaints stay under threshold.
4. Pause and investigate if deferred rate rises or inbox placement drops more than 10 points.

Common mistakes that still block inbox delivery

Most deliverability fixes fail because one small habit re-creates the problem, even when SPF and DKIM pass. One mistake can erase a clean list.

Say you fixed authentication and cleaned the list, then bought 1,000 new leads to hit a goal. Picture bounce rate spiking to 5% and the next three campaigns landing in spam despite good content.

You cannot buy your way to inbox. Purchased lists carry traps and stale addresses that burn reputation for weeks. You also cannot hide behind a free mailbox. Sending bulk from @gmail.com or @outlook.com fails alignment and looks like spoofing.

The quiet killer is stale data. Old lists, copied spreadsheets and role addresses sit until they bounce. Validate before every large send and let non-engaged contacts go.

• Mistake: buying or renting lists -> what to do instead: grow with double opt-in and confirm new addresses with validation
• Mistake: mailing hard bounces again -> what to do instead: suppress hard bounces permanently after one failure
• Mistake: using link shorteners and heavy images -> what to do instead: link to your domain and keep one clear CTA
• Mistake: sending from multiple new domains -> what to do instead: warm one domain and keep volume steady
• Mistake: ignoring List-Unsubscribe -> what to do instead: offer one-click unsubscribe and honor it in hours

Questions people still ask

I have cleaned lists that bounced at 6% and watched inbox return after fixing SPF and dropping the dead weight first.