There are many reasons as to why your email is being marked as spam by the recipient's email server, but the main cause for this is you are currently running your mail services from the shared server as a result there is more chance of your server IP being marked as spam as it is used by many users.
For now, you need to ask your recipient to check their spam folder and mark your email as "Not Spam", so from next time your message will be sent to the inbox folder and not to the spam folder.
We recommend you use our dedicated email services or google's email service google workspace to avoid such problems as these.
Ghurkha host email services:https://gh.thulo.com/email-office.php#business
Google's email service:https://gh.thulo.com/workspace-by-google.php