Couple of days back someone used our domain to send spam emails, Now we are using mailgun to send emails but none of email is going to inbox, because previously it was involved in spam activity, how we can now prevent this issue that our email should land to the inbox folder right away! We have other domains to for the purpose of sending emails we can use those too!
It's a matter of notoriety of domain and IP address. If you use another domain on the same server (ip address), it will end up in the spam folder too.
Using a mail relay like mailgun, and especialy with a dedicated IP option, will help over time to get out of the spam folder if not right away.
You can also help fix your issue by asking some of your users to mark your emails as "not a spam".
No other quicker solutions.