Do not perform AAAA queries

[essays-on-esotericism]

senderscore does not publish AAAA records. Validity last year changed the terms for their score.senderscore.com service to allow only 10,000 queries per 30 days for anonymous users - by searching for AAAA records first (that will inevitably be empty), we functionally cut that limit in half.

The "ip4" argument explicitly instructs net.LookupIP to retrieve only A records for the specified hostname.