For a case, I need to check whether the DNS of an e-mail address is valid. For example, firstname.lastname@example.org is valid, where email@example.com isn't. There are several services to do a DNS check. For example this one and this one. Unfortunately, these services are not for free, limited to a number off calls, already shut down of something else. Can anyone recommend a service that does this or has a module almost ;) available in the appstore?