clients.l.google.com
Hi, clients.l.google.com is on the YouTube ad list
However this is a needed domain
It is a CNAME for clients1.google.com and clients5.google.com which are needed by Google services like Maps and Drive and Gmail
If you use PiHole with Deep Packet Inspection on, CNAMEs get blocked too
One thing clients4.google.com is needed for is Chrome
By blocking clients.l.google.com, you are blocking everything that is also a CNAME if the end user uses Deep Packet Inspection like I am.