Thank you for leaving a comment, @rcgotts.

There are only certain emails that work with secure WebMail in QuickBooks Desktop. That's the reason why it isn't appearing in the drop-down menu when setting up your email.

Here's a list of supported emails per QuickBooks version:

• For QuickBooks 2019 and 2020: Available for Gmail, Yahoo Email, Windows Mail, Hotmail, and AOL. (Mozilla Thunderbird Email Client*) *Supports plain text version in Mozilla.
• QuickBooks 2018: Available for Gmail and Hotmail/Live users.
• QuickBooks 2017 R5 and newer: Available for Gmail users. Not available on earlier versions.

However, it's possible to manually add an email provider in QuickBooks Desktop. But you'll need to contact your email provider for the Server Name and Port number that needs to be used to set it up.

I'll guide you how to manually add email provider:

1. Go to Edit.
2. Choose Preferences.
3. Select Send Forms.
4. Under Company, tick the WebMail.
5. Click Add.
6. Pick Others under the Email Provider.
7. Enter the Server Name and Port and a valid Email address.
8. Hit Ok.

You'll also want to learn about common errors in sending emails in QuickBooks Desktop: Fix Common Errors in Sending Emails QuickBooks Desktop. 

Get back here in the Community if you've got some concerns. I'll be more than glad to help. Have an awesome day!