Imagine a SaaS company with 100,000 contacts in its database.

The marketing team sends a weekly newsletter and product promotions. Sales uses Apollo to reach potential customers. The product sends password resets, payment receipts and account notifications.

Every now and then, marketing runs a re-engagement campaign to people who haven't opened an email in six months.

Four different sending activities. Three teams. One domain.

Nobody thinks much about it until newsletter engagement starts dropping, some customers report missing password resets, and Gmail spam complaints begin creeping up.

The problem isn't necessarily the volume. It's that nobody has a clear picture of what's being sent, who's receiving it and how each activity affects the others.

Let's look at what's happening behind the scenes.

Marketing sends newsletters and promotions from [email protected] to its 100,000 contacts.

Sales sends cold outreach through Apollo using [email protected]. Some recipients have never heard of the company.

Product sends password resets, billing notifications and account updates from the same domain. Customers expect these emails to arrive immediately.

Marketing again launches a re-engagement campaign to inactive subscribers, hoping to bring some of them back.

Each team has its own goals. Marketing wants more revenue, sales wants more meetings, and product wants customers to have a smooth experience.

But mailbox providers don't necessarily see these activities as completely independent.

When recipients complain about unwanted emails, it can affect the sending reputation associated with the domain and related infrastructure.

And that's where things get complicated.

It depends on how the company sends email.

If you're sending one newsletter to 100,000 people who explicitly subscribed, and your transactional emails are properly configured, you might not have a problem at all.

You don't need five domains, ten subdomains and an expensive deliverability setup just because someone told you that's best practice.

But if you're mixing cold outreach, marketing campaigns, transactional messages and poorly managed re-engagement campaigns, you need to understand the risks.

Here's what could happen:

The real cost isn't just a worse deliverability score. It's lost revenue, missed opportunities and customers who can't receive emails they actually want.

I wouldn't start by buying another domain or moving everything to a new email platform.

I'd start by understanding what the company already has.

I'd ask each team three questions:

I'd include tools that are easy to overlook: Apollo, HubSpot, Stripe, customer support software and any internal product integrations.

The goal is to build one complete picture of the company's email activity.

This is probably the most important part.

The company's 100,000 contacts aren't necessarily one audience.

Some people subscribed to the newsletter. Some are existing customers. Others are sales prospects who have never opted into marketing.

These groups have different expectations.

I'd make sure newsletter subscribers receive marketing emails, customers receive transactional messages, and cold contacts aren't automatically added to the newsletter database.

I'd also review inactive subscribers and introduce sunset rules for people who no longer engage.

Adding subdomains won't fix a problem caused by sending unwanted emails to the wrong people.

Once I understand the setup, I'd look at separating sending infrastructure.

For example:

This makes sending activity easier to organise, monitor and troubleshoot.

But there's an important distinction: separate subdomains don't guarantee complete reputation isolation. Mailbox providers can consider signals across related domains and infrastructure.

The objective isn't to hide bad sending behind another domain. It's to make sure every sending stream has a clear purpose and responsible owner.

I'd establish a baseline before making any changes.

That means looking at:

I'd also check Google Postmaster Tools to understand how Gmail sees the sending domain, where sufficient data is available.

Then I'd monitor performance as the new structure is introduced.

Don't move everything overnight and start sending hundreds of thousands of emails from a new subdomain.

Build volume gradually, starting with your most engaged recipients.

This is the part companies often forget.

Marketing owns campaigns. Sales owns prospecting. Product owns customer notifications.

But who owns the overall email operation?

Someone needs to understand how all these activities fit together, monitor their performance and make sure one team's decisions don't create problems for everyone else.

Without that ownership, the same mess will eventually come back.

If your company sends one newsletter, has a clean subscriber database and properly configured transactional emails, don't overcomplicate things.

A separate domain for every sending activity isn't automatically better.

But if several teams are sending different types of email without knowing what's happening across the organisation, it's worth investigating.

You don't need to wait until Gmail starts putting your newsletters in spam or customers complain about missing password resets.

Start by finding out who's sending email from your domain right now.

Reply to this email with your main sending domain, the subdomains you use and which teams and platforms send from each one.

I'll tell you what I'd look at first and where I see the biggest risks.

Best,

Pavel