I've no direct experience of Sage 200, but "Transaction Email" is something that was introduced in the 50 series a long time ago. It's not, as you might think, a straightforward system to "email the invoice to the customer" but a system to email the invoice to the customer's accounts software - i.e. if the customer has a compatible system, it can take those emails and from it create the necessary transactions within the software. I can't imagine they'd use the same name for something different on 200, so I'd expect it to be the same on that.

Assuming 200 works in a broadly similar way to 50, what you really need to look at is the template/layout design for the invoices themselves and, in the properties, look for email options. You'll need to give it access details for your SMTP server (or I think it can work via Outlook, but I don't use that), and configure a few other options - and then when you run the report, you should be able to email it (and therefore the invoices) as one of the run options or, if you preview it, there may be an "email" button along the top.

You might also have an "Email" icon on your invoicing screen, which can have a specific report linked to it (ideally the invoice layout you've set up for emailing, obviously) - after which you'd be able to email invoices by highlighting them and clicking on that.

Sorry that's all a bit vague - not only, as I said, do I have no direct experience of 200, but I don't have 50 in front of me for precise details (which might differ anyway in the bigger package).