If you're sending email campaigns and seeing no results, the problem usually isn't the content — your mail isn't reaching the inbox at all. This article covers the technical setup that decides that.
Why email gets marked as spam
Receiving servers (Gmail, Outlook) ask one question: is this message really from the domain it claims? Without proof, the default is suspicion — which means the spam folder, or outright rejection.
That proof is three DNS records, and you need all three — any one of them alone is not enough.
SPF: who is allowed to send as you
An SPF record lists the servers permitted to send mail for your domain. When Gmail receives a message claiming to be from yourdomain.com, it reads your SPF record and asks whether the sending server is on the list. If not, the message is suspect.
The most common mistake: more than one SPF record on the same domain. There must be exactly one, combining every provider you use. With two, both are ignored and the result is the same as having no SPF at all.
DKIM: a digital signature for your mail
DKIM adds an encrypted signature to every message header. The receiving server checks that signature against a public key published in your DNS. If it matches, the message is authenticated.
What separates it from SPF is that it also proves the message content wasn't altered in transit, and it survives forwarding — which is exactly where SPF alone falls down.
In Mersal the steps are simple: from Sending domains you add your domain, the system generates the DNS records you need, you add them at your domain provider, and come back and press "Verify".
DMARC: the policy that ties them together
DMARC tells the receiving server what to do when a message fails both SPF and DKIM — and sends you reports on every attempt to send as your domain, including spoofing attempts.
Start in monitoring mode only:
v=DMARC1; p=none; rua=mailto:[email protected]
Leave it a month and read the reports. Once you're satisfied every legitimate sending source passes, move to p=quarantine and then p=reject. Jumping straight to reject without monitoring will block your own legitimate mail.
Bulk sender rules (Gmail and Yahoo)
Since 2024, anyone sending more than 5,000 messages a day to Gmail or Yahoo addresses must have:
- SPF and DKIM configured and passing.
- A DMARC record, even at
p=none. - One-click unsubscribe in the message header, honoured within two days.
- A spam complaint rate below 0.3%.
That last number is the one that matters most: one complaint per 333 messages is enough to get you filtered. Which is why a clear unsubscribe link isn't an optimisation — it's protection.
Tracking domains
When open and click tracking runs from a domain shared with hundreds of other senders, your reputation is tied to theirs. A custom tracking domain makes tracking links come from your own domain — which improves deliverability and looks professional instead of showing strange-looking links.
Use a dedicated subdomain such as link.yourdomain.com rather than your root domain, so any link-reputation problem can't spill onto your ordinary company mail.
How to tell your mail is going to spam
- Send to yourself on three providers: Gmail, Outlook and Yahoo. If only one filters you, the problem is specific to that provider.
- Open the message header: in Gmail via "Show original". Look for
spf=pass,dkim=passanddmarc=pass. Any fail is your answer. - Watch the open rate: a sudden drop from 25% to 5% with no content change is a delivery problem, not a subject-line problem.
- Register with Google Postmaster Tools: it shows your domain reputation at Gmail and your complaint rate as real numbers.
Things in the message itself that raise spam risk
- An email that is one big image with no text — one of the oldest spam signals there is.
- Short links from free shared shortening services.
- Attachments, especially archives or executables.
- A
no-reply@reply address — it suppresses engagement and raises complaints. - A low text-to-image ratio, and words like "FREE" and "WIN" in caps with exclamation marks.
Warming up a new domain
A new domain has zero reputation. A practical schedule:
- Days 1–3: 50 messages a day to your most engaged customers — the ones who genuinely open.
- Days 4–7: 200 a day.
- Week 2: 500 a day.
- Week 3 onward: double weekly while complaints stay under 0.1% and bounces under 2%.
Always start with your most active segment. Early opens build positive reputation faster than anything else you can do.
Beyond the technical setup
Authentication is necessary but not sufficient. The other factors:
- List quality: sending to dead addresses raises your bounce rate and damages reputation. Mersal keeps bounce logs and suppression lists — review them and remove failing addresses.
- Address validation: the system can check an address before sending: syntax, MX record, disposable addresses, common typos, and role addresses (info@, sales@).
- Warm-up: a new domain must start with small volumes and increase gradually, exactly like a WhatsApp number.
- Easy unsubscribe: a clear unsubscribe link reduces spam complaints, and spam complaints are the single most damaging signal.
A checklist before your first campaign
- Add your sending domain, enable DKIM, and confirm verification passed.
- Confirm you have exactly one SPF record covering Mersal and every other provider you use.
- Add a DMARC record at
p=nonewith an address to receive reports. - Configure a custom tracking domain.
- Run address validation across your list and clean it.
- Send to 50 addresses first and check delivery before mailing the whole list.
Frequently asked questions
How long does a DNS record take to work? Usually minutes to an hour, occasionally up to 24 hours depending on your domain provider.
My reputation is already damaged — what now? Stop mailing cold lists entirely, send only to your most engaged 10% for two weeks, and purge every bounced address. Reputation does recover, but slowly.
Should campaigns use my main domain or a subdomain? A subdomain such as mail.yourdomain.com is safer: any campaign reputation problem stays away from your day-to-day company mail.
