All emails end up in Junk/Spam box

There’s no fool-proof way to “ensure” they don’t end up flagged as spam, but you can take some measure to help.

First would be don’t use the default “from” address. Use a real address that has a domain matching your site’s domain. You can set a “from” address in the plugin’s settings under the Emails tab.

Second would be to add the from address in the header. WP’s wp_mail function does not include this by default. There is a filter for the plugin to add/change headers. See the wpmem_email_headers filter for more info.