TheHarvester is another reconnaissance tool. This one can gather emails, subdomains, hosts, employee names, open ports and banners from different public sources. Basic usage is pretty simple:

theHarvester -d <my.Domain> -l 500 -b all

This will output a lot of data. To output this to a file, so you can read it later, use the following command:

theHarvester -d <my.Domain> -l 500 -b all -f harvestedInfo

This will output a file containing the information that TheHarvester gathered in an SQLite file. This makes reading the outputs fairly easy.