Adding external participants to a course does not work

[maxi-k]

Describe the bug
As a course admin, I see an option to add external participants to the course on the admin page by entering a name and an email address.
The input placeholder text indicates that it is possible to add external mail addresses here, and that they should receive an invitation mail.
When I test this with one of my private email addresses, I don't receive an email and there's no indication that anything happened.

To Reproduce
Steps to reproduce the behavior:

1. Go to the admin page of a course you administrate
2. Scroll down to the "External Participants" section
3. Add a name and private email address you know exists (I checked multiple providers)
4. Click "Submit"
5. Check every spam folder, observe no invitation mail exists
6. Klick the "Show Invitations" Link in the "External Participants" section; there are no invitations there either

Expected behavior
I expected an invitation mail to arrive at the email account I tested this with, and maybe some kind of data to appear in the 'invitations' section.

Desktop

• OS: Ubuntu 22.10
• Browser: Firefox
• Version: 111

Additional context
I checked the networking tab using the browser inspection view.
This seems to POST form data to /api/course/{cousrseId}/createUserForCourse and always returns 200 OK.

[karjo24]

I'm not able to reproduce this. @joschahenningsen do you know whether you could repro this at the time of self assigning this or not?

[karjo24]

Anyways, I'll fix the bug that "show invitation" doesn't actually show anything.

[joschahenningsen]

I cannot recall, I remember having implemented a new email queuing table

gocast/dao/email.go

Line 18 in f4bf941

Create(context.Context, *model.Email) error

for inviting admins to their lectures, which works reliably. We should use it also for inviting external participants.

[karjo24]

We should use it also for inviting external participants.

You already changed the respective functions so external participants are invited via the email queuing table in June of 2023.