This is a summary, not legal advice, and the rules differ by jurisdiction. Take proper advice for your situation.
The general shape of it
- Publicly published business contact details are treated differently from personal data in most regimes, but they are not unregulated.
- Legitimate interest is the usual basis for B2B outreach in the EU and UK, and it requires the contact to be relevant to their role.
- CAN-SPAM (US) is mainly about honesty: real sender, real address, working opt-out, no deceptive subject lines.
- An unsubscribe that works is non-negotiable everywhere, and honouring it promptly matters as much as offering it.
The practical rules
Contact people about things plausibly relevant to their job. Say who you are. Make opting out trivial and permanent. Keep a record of where the data came from. Do not email individuals about things unrelated to their professional role.
Where tools help
Filtering by business versus consumer mailbox is a compliance tool as much as a commercial one: consumer addresses carry meaningfully different obligations.