If I have an opportunity, that is with an account with a primary contact (with an email address), and the opportunity has a contact specified (different from the primary contact on the account), and I create an email from the timeline, it adds the contact listed on the opportunity as the TO address. As you would expect.

However, when using the price offer Export to PDF > Email, it populate the TO address with the Account, NOT the contact.

As a rule, accounts will not normally have email addresses (as you don't email an account, you email a person)

Moreover, this Account being listed doesn't even inherit the email property of primary contact of the account so if no email address is recorded directly on the account (we don't even have an email field on the account), therefore this would generate an error message.

My suggestion would be that if a contact is specified on a record (such as price offer), that emailing from that record always picks up the contact as the TO: address, and NOT the account.