An SPF or Sender Policy Framework record is a DNS record for your domain that validates emails sent from your domain. This improves the deliverability of your messages and helps prevents them from being marked as spam.
SPF is a type of TXT record, so you will need to manage your TXT records. The default SPF record for Hostinger Email is as follows:
v=spf1 include:_spf.mail.hostinger.com ~all
If your domain is pointing to Hostinger by nameservers, you can set correct email DNS records from hPanel: just go to Emails → domain name → DNS settings and click on Set all to default:
In case you are using Titan Email, before you add new values make sure to delete any old value of SPF records.
Just create the following TXT record on your domain's DNS Zone:
v=spf1 include:spf.titan.email ~all
You can also check this article: How to set up a domain for Titan Email?
If your domain is pointing elsewhere by nameservers, the SPF record needs to be set up from the service to which you are pointing your domain.
Once the SPF record is successfully added propagation will start, which can last up to 24 hours to fully propagate.