Internet? Emails?

Since I swapped the hard drive on my laptop, my emails, even those without attachments, got stuck in the Outlook outbox.

Is it the network operator's fault or the Wi-Fi cube?

Have a look in your Outlook settings to see if "automatic sending and receiving" is checked. Do you work with the mail program supplied with Windows 10 or do you have a separate Office Outlook?

Outlook is probably configured incorrectly as far as the outgoing server is concerned.

Whatever a "WLAN cube" is.

Neither the WLAN cube nor the network operator were changed by changing the hard drive.

Do you have a network connection, can you surf the Internet? Can you receive mail? If so, it is probably not the WLAN. Just check the configuration of Outlook.

Mails arrive, I can surf too. The network connection works.

How do I find the configuration of Oullook?

Mails arrive, I can surf too. The network connection works.

It's that easy to rule out WLAN as the cause.

How do I find the configuration of Oullook?

I guess under File → Options or something. I don't use Outlook and I haven't installed it either. Your mail provider may also have a help page that describes how to configure Outlook. Possibly. A search engine also helps.