[Exim4U] DNSBL question

I hope everyone is well, it has been a long while. I am wondering if others use DNSBL and what they might do about random ip addresses that show up on the Zen DNSBL such as cell phone provider IP's that get used for people to send email from their cell phones? I have run into it twice now, once with ATT and again with T-mobile. Also, how to ensure that DNSBL lookups are turned off? And what provides the functionality? I think it is exim directly, and within the acl's? or does exim4U do it a bit differently? Thx for any and all info/answers. Helmut