What is the difference between transactional and marketing email?
Receipts and notifications are not marketing, and mixing them creates real risk.
A transactional email is a message the recipient expects because of something they did: a receipt, a password reset, a shipping notice, an appointment confirmation. A marketing email promotes something. The moment you add a promotion to a receipt, it is a marketing email.
Why the distinction matters
Marketing email carries obligations that transactional email does not. The FTC's CAN-SPAM compliance guide distinguishes between commercial content, which advertises or promotes a product or service, and transactional or relationship content, which facilitates a transaction or updates a customer about an existing one. The guide's rule is that the primary purpose of the message determines which set of requirements applies. A receipt with a coupon stapled to the bottom has a mixed purpose, and you should assume it is commercial.
Practically, that means unsubscribes. A marketing email needs a clear opt-out and a valid physical postal address. Transactional email does not, and it should not be suppressible, because a customer who unsubscribed from your newsletter still needs their password reset.
The operational reason to keep them separate
Transactional mail has very high engagement. Marketing mail has lower engagement and generates complaints. Sending both from the same identity means your marketing complaints can drag down the deliverability of the receipts people actually need. Many teams separate them by subdomain so the reputations do not mix, which also makes the reporting readable.
In HubSpot specifically
HubSpot separates marketing email from transactional email, and transactional sending may require a separate add-on depending on your subscription. Check current terms with HubSpot or with us before you design a flow that depends on it, rather than discovering the limitation after the build. If your transactional mail is generated by an application rather than by the CRM, it usually belongs with your product or service platform anyway. Our Service Hub guide covers the service-side messaging, and HubSpot Free vs Starter covers what the lower tiers include.
The practical test
Ask what the recipient would say if you asked them why they got it. If the honest answer is because I bought something and this confirms it, it is transactional. If it is because you wanted to sell me something else, it is marketing. When it is both, treat it as marketing. This is general guidance, not legal advice.
Related: What HubSpot Hubs do you work with?. What HubSpot services does LevelUp Digital offer?. Can LevelUp Digital build custom HubSpot integrations?.