Android-PrivateDNS

3. Add a provider that offers secure DNS

This is where it can get a bit tricky. You need to have the address of a provider that offers Private DNS. Here's my provider of choice: 

1dot1dot1dot1.cloudflare-dns.com

Some other possible hostnames you can use:

• Google DNS: dns.google

• Quad9: dns.quad9.net

• Cleanbrowsing DNS: security-filter-dns.cleanbrowsing.org

• Open DNS: 208.67.222.222

• NextDNS: 45.90.28.0

• Comodo Secure 8.26.56.26

• OpenNIC: 192.95.54.3

Note: Although the above free DNS services are all worth trying, I recommend going with Cloudflare (1dot1dot1dot1.cloudflare-dns.com). I find it the fastest and the most secure of the bunch. On top of the speed, Cloudflare adds DNS filtering into the mix, which can help prevent email from being sent from malicious IP addresses.