Unfortunately there is nothing we can do if it lands on the spam because it actually depends on your mail server. But I would suggest that using a transactional mail service e.g. https://sendgrid.com/

It might be some of the possibilities why your e-mails lead into spam folder.

1. Your domain has been somehow blacklisted.

2. You are using PHP Mailer to send e-mails which most email providers consider as unreliable.

3. Your email server's IP address has been marked as spam.

Services like https://sendgrid.com/ provides email delivery services and allows you to setup SMTP authentication in your Joomla global configuration. Most of the time, e-mails delivered by these transactional e-mails would lead into the inbox.

In the event that the emails are also flagged as spam, you could get in touch with their support to look into this