You've just imported a list into HubSpot. Maybe it came across from your old CRM during a migration. Maybe it's a list your team collected at an event. Maybe it's an export someone dug out of a folder from two years ago. Either way, it's in your portal now, and someone wants to email it.
That first send is the riskiest email you'll send all quarter.
Imported lists are the lowest-quality data you will ever put into HubSpot. They're full of typos from form fills, role addresses like info@ and sales@, people who left their jobs eighteen months ago, and addresses that were fine when the list was built but aren't any more. And HubSpot won't stop you from emailing any of it. It checks that an address looks like an address on import. It doesn't check that the mailbox actually exists.
So the moment to validate isn't after the bounces roll in. It's now, before the list touches an active list or a send.
A hard bounce in HubSpot is close to permanent. When a contact hard bounces, HubSpot marks them and stops sending them marketing email, and getting that reversed is deliberately hard. So a dead address you email once isn't just a wasted send. It's a contact you've effectively burned.
The bigger problem is what a bad send does to the addresses that are good. Mailbox providers watch your bounce rate as a signal of whether you know who you're emailing. Send a freshly imported list with 20% dead addresses in it, and you don't just lose the 20%. You drag down deliverability for the whole database, including the customers and pipeline you actually care about. One bad import can undo months of careful sending.
It's worth being precise about this, because most people assume HubSpot is doing more than it is. When you import a list, HubSpot runs a few basic checks and waves everything else through.
What HubSpot checks:
@, a plausible domain, no illegal characters. Rows that are obviously malformed get rejected on import, or by the Import API.What HubSpot does not check:
In other words, HubSpot confirms an address is shaped correctly. It never confirms an address is real. That gap, between "looks like an email" and "is a mailbox someone reads", is exactly what validation exists to close.
Before you run anything, it helps to know what an email validation tool can and can't tell you.
Being honest about the limits here saves you from trusting a result more than you should.
Validation reliably catches:
@, malformed addresses that never had a chance.info@, admin@, sales@. Often deliverable, but low-engagement and higher-risk, so worth flagging rather than blindly sending to.The honest limit is the catch-all (or "accept-all") domain. Some mail servers accept every address at the domain whether the mailbox exists or not, so no validator on earth can be certain a specific inbox is live. You'll get a result like unknown or accept-all rather than a clean valid. That's not the tool failing. It's the tool telling you the truth about what can't be known from the outside.
And validation can't tell you whether the person still works there, whether they want to hear from you, or whether they'll engage. It confirms an address is deliverable. That's the job. It just isn't the whole job of a healthy list.
Here's the sequence that keeps a dodgy import from ever reaching a send.
The order matters. Every step before step five is about making sure the send in step five is safe.
There are two moments you can do this, and they trade off against each other.
Validate inside HubSpot, after import. Bring the list in, then validate the records where they live and segment on the result. For most teams this is the one to reach for. It's HubSpot-native, so there's nothing to run in a separate tool and nothing for anyone to forget. And it leaves something behind: the validation result is written to the contact record as a property you can filter, report and build workflows on. Validate an address once and its status stays there, so the next import that includes the same person doesn't get checked again. You don't pay to validate anyone twice, and every future import gets a little cheaper and faster as your store of already-validated addresses builds up. The honest trade-off is that the unverified addresses do land in your portal before you clean them, so the discipline of holding the send (step one above) is what keeps a dead record from ever becoming a billable marketing contact.
Validate before import. Clean the file first and only bring the deliverable addresses into HubSpot. This keeps the portal spotless and means a dead address never gets the chance to become a marketing contact or record a hard bounce, because it's never there in the first place. The cost is that it's an extra step outside HubSpot, you lose the invalid records entirely (which matters if you wanted them for a non-email reason), and the check happens somewhere HubSpot can't see, so it doesn't build the on-record history that saves you from re-validating the same addresses next time.
For imports you run regularly, or any time you're building an ongoing process rather than doing a one-off, validating inside HubSpot tends to win: it's repeatable, the results compound, and nobody has to remember to do anything outside the tool. Keep the validate-before-import route for the genuinely untrusted one-off, like a large cold or purchased list you'd rather never let near your portal or your sender reputation at all.
Validating an imported list is the bulk cleanup. It's half the work.
The other half is that new addresses keep arriving. Every form submission, every enrichment pass, every future import adds email that hasn't been checked. Clean the migration list once and do nothing else, and you'll be back where you started within a few campaigns, wondering why your bounce rate is creeping up again.
The teams who keep deliverability healthy treat validation the way they treat deduplication: a bulk cleanup to fix what's already there, then an ongoing process running in the background to catch new problems as they arrive, so the mess never rebuilds. The import is where you start. It isn't where you stop.
Does HubSpot validate email addresses on import? Not in the way you'd want. HubSpot checks that an address is correctly formatted, but it doesn't verify that the mailbox actually exists. You can import forty thousand addresses, including dead ones, and HubSpot will let you email every one of them.
What happens if I email an imported contact that hard bounces? HubSpot marks the contact as hard bounced and stops sending them marketing email, and reversing that is deliberately difficult. Worse, repeated hard bounces from a single send signal to mailbox providers that you don't know your list, which lowers deliverability for the good addresses too.
Should I validate before importing or after? For most teams, validate inside HubSpot after the import. It's native, it's repeatable, and the result is written to each contact record, so you never pay to check the same address twice and every future import gets faster. Keep the validate-before-import route for a genuinely untrusted one-off, like a large cold or purchased list you'd rather never let into your portal at all.
Can email validation guarantee an address is deliverable? No, and be wary of any tool that claims otherwise. Catch-all domains accept mail for every address whether the inbox exists or not, so those come back as unknown rather than valid. Validation dramatically reduces your bounce risk. It doesn't eliminate it entirely.
How many addresses in a typical imported list are actually bad? It varies a lot by source. A carefully kept house list might only be a few per cent stale. An old export or a purchased/rented list can run well into double digits. The only way to know for your specific list is to validate it, which is exactly why you do it before the send, not after.
Before your next import goes anywhere near a campaign, run it through validation and see what's actually in there. Koalify validates imported contacts in bulk inside HubSpot, so the dead addresses get caught at the door, not after they've bounced and taken your deliverability down with them.
Start with the HubSpot email validation guide if you want the full picture first.