How can I get a receipt that the email I sent was read?

You can't (short of asking). The best you can get is a message that their email provider forwarded the message to their inbox.

There is nothing in the email protocol that supports actual read receipts. It also doesn't require that the email server respond to your disposition request. Many will not as it is just extra overhead that they can easily just not deal with.

typically this is only an inter-company thing.

Ask the recipient to let you know when they received and read the email. Don't expect many recipients to respond to your request.