he HP scan to email feature does not use Thunderbird in any way. It acts as it's own mail client and submits the mail directly to the SMTP server. This is the same procedure Thunderbird follows when you click the send button. but at no time does Thunderbird interact with the printer.

If you have an IMAP account with Gmail or Outlook.com configured in Thunderbird, the sent mail that they send from the HP printer using their SMTP server will appear in Thunderbird through synchronization, but this is a unique feature of these two mail providers, not mail in general.

The causes of mail not being sent from the HP device are probably very similar to those that cause Thunderbird not to be able to send mail. Anti virus packages / Internet security suites and their firewalls Security software from banks and other agencies Routers that block access to the HP device to the internet.

In my home my HP printer operates it's own wireless network that allows devices to interact with it. That network however has no access to my internet router thus no send to email option as it does not actually connect to the internet. Perhaps your internet gateway device also is not configured to allow the HP device access, or the HP device does not have the correct password to access your local wireless network and hence the internet.

In any case, this is not a Thunderbird issue.

Confirmation-mail are (mostly) denied in setup by the receiver. A good reason is to not let spammers know an address is alive. If you try to send yourself an email with confirmation and it doesn't work, check the individual Tools/ account setup / return receipts or the global settings in Tools / option / advanced /general / return receipts

HP printer, Do you send from your PC's email-client (Thunderbird) or from printers email client? Can you save a scan to your PC and then send it?

What do you mean by printer recognizing TB?

@MATT Sorry didn't see you answering.