An email campaign is a coordinated series of emails sent to a defined audience to achieve one specific goal. What makes it a campaign rather than a collection of emails is that the messages are planned as a set, sent on a deliberate schedule, and measured against a single outcome.
Published by emailcampaign.ai, which builds sending infrastructure for outbound email. We run one of the six types below and say so where it matters.
The five common types
| Type | Goal | When it sends | Typical length |
|---|---|---|---|
| Welcome series | Onboard, set expectations, build early habit | Triggered when someone signs up or subscribes | 3 to 5 emails |
| Promotional | Drive a purchase or a specific action | Scheduled around a launch, sale or season | 1 to 3 emails |
| Transactional | Deliver information the person is waiting for | Instantly, on a specific user action | 1 email per event |
| Newsletter | Stay present, build authority, hold attention | On a fixed rhythm, weekly or monthly | Ongoing |
| Re-engagement | Recover subscribers who stopped opening | Triggered by a period of inactivity | 2 to 3 emails |
Campaign and automation get used interchangeably, and the practical difference is what starts them. A promotional campaign starts because you decided today is the day. A welcome series starts because a person did something. That distinction matters mainly because it changes who controls the timing.
The sixth type, which behaves differently
Cold outbound is a campaign by every definition above: a coordinated series, a defined audience, one goal. But it differs on the thing that determines whether any of it arrives.
Every type in the table goes to people who opted in. Cold outbound goes to people who have never heard from you. That single difference changes the legal basis, the infrastructure, the sending volume and the metrics, which is why tools built for one category refuse to serve the other.
| Opt-in campaigns | Cold outbound | |
|---|---|---|
| Audience | Subscribers who asked | People with no prior relationship |
| Sending identity | One domain, one platform | Many mailboxes across separate domains |
| Volume per identity | Thousands per send | Eight to ten a day per mailbox |
| Primary metric | Click rate and revenue per send | Reply rate and meetings booked |
| Typical platform | Mailchimp, Klaviyo, Brevo, HubSpot | Dedicated outbound tooling |
| What failure looks like | Rising unsubscribes | A burned sending domain |
Worth knowing if you are considering it: the opt-in platforms prohibit cold sending in their terms and enforce it by suspending accounts. That is not pedantry. They send from shared IP pools, so one customer’s complaint rate degrades placement for everyone else on the pool.
The part most guides skip
Choosing a campaign type is easy. The decision that actually costs people is which campaigns share a sending domain.
Mailbox providers attach reputation to the domain in your From address. Your transactional email, which is opened almost every time and complained about almost never, contributes to the same history as your promotional sends and anything else going out under that name. The provider does not know which internal system produced which message. It sees one domain with one blended record.
That is why the failure is always asymmetric. Transactional mail is the best behaved traffic you have, and it is the traffic that gets hurt, because it is the traffic that could least afford it. A password reset landing in spam is a support problem, a security problem and a churn problem at once.
Separate by risk rather than by team:
| Domain | What sends from it | Risk |
|---|---|---|
| yourcompany.com | Corporate mail only | Protect at all costs |
| mail.yourcompany.com | Transactional: resets, receipts, alerts | Must never fail |
| news.yourcompany.com | Newsletter and promotional, opt-in only | Moderate |
| a separate registered domain | Cold outbound | Expendable by design |
The first three are subdomains deliberately, because a subdomain inherits some standing from a healthy parent. Cold outbound gets a separately registered domain precisely so that inheritance does not run in the other direction. When a cold domain burns, it should burn alone.
What decides whether a campaign lands
Whatever the type, the order of weight is the same, and content is not near the top:
- The sending domain’s history. A domain with no past gives a filter nothing to read, and a domain that suddenly sent four hundred messages has given it something worse than nothing.
- Authentication that resolves. Not merely exists. Two SPF records on one host is a permanent error, and so is an include chain past ten DNS lookups, and both look perfectly fine in a registrar dashboard. Checking the full tree takes about thirty seconds.
- Hard bounce rate. Above roughly two percent, a receiver reads the list as bought or stale.
- Complaint rate. Google publishes the threshold: below 0.1 percent, never reaching 0.3.
- The message itself. Last, which is why rewriting a subject line is the first thing most people try and the last thing that helps.
Measuring one honestly
Open rate has been unreliable since 2021, when Apple Mail Privacy Protection began pre-loading images on recipients’ behalf and registering opens that no person performed. Corporate security scanners do the same. For opt-in campaigns, judge on clicks and revenue per send. For cold outbound, judge on replies and meetings booked, both of which require a human to act.
Questions, answered straight
- What is an email campaign?
- A coordinated series of emails sent to a defined audience to achieve one specific goal, such as onboarding a new customer, announcing a product, or booking a meeting. The defining feature is that the messages are planned together and measured together, rather than sent one at a time.
- What is the difference between an email campaign and an email automation?
- A campaign is usually tied to a moment and sent to a segment you choose, such as a product launch going out on a set date. An automation runs continuously and is triggered by a person's behaviour, such as a welcome series that starts when someone signs up. Many tools use the words interchangeably, which is why the distinction is worth stating.
- What are the main types of email campaign?
- Five cover almost everything: welcome series, promotional, transactional, newsletter, and re-engagement. Cold outbound is a sixth that behaves differently enough to need its own infrastructure.
- How many emails should an email campaign contain?
- It depends on the type. A welcome series is typically three to five. A promotional campaign is often one to three. A cold outbound sequence works best at three or four. Longer is rarely better, and for cold outreach it actively raises complaint risk.
- Can all email campaigns be sent from the same domain?
- No, and this is the mistake that costs the most. Transactional email must never share a sending domain with cold outreach, because a reputation problem on the outbound domain would take your password resets down with it. Separate by risk profile.
Published 20 September 2026. Updated 20 September 2026. Written by the team that runs the infrastructure; numbers come from the platform's own provisioning and sending, and from the providers' published documentation at the time of writing.