MX records determine which service provider you are using for your emails, and where to deliver emails to.
So if you set MX records different from the default ones for your email service, be it Hostinger Email or Titan Email, you won't be receiving any new emails to your email accounts. However, in the case of Hostinger Email, you will still be able to create new email accounts and send emails.
In case you want to set your MX records again, it can be easily done via hPanel.
Applying new MX records takes up to 24 hours