try to send an email to support@itch.io but outlook returns an error message that the message cannot be sent.

Does anyone have the same issue? is there another way to contact their support?

You can try to ping the official Twitter account if that's an option, but you should troubleshoot your e-mail setup, otherwise support can't do much. I'll ask an admin as well.

We are currently experiencing no issues on our end regarding email acceptance for our support system. You may want to ensure you’ve typed the email address correctly and that your outlook is configured correctly and your account is not restricted from sending mail in any way.