I emailed a rental application for an apartment to a potential landlord. I've spoken with them over the phone, saw the unit in person and they emailed the application and I emailed it back (because I live out of state)... along with personal information like my drivers license and paystubs. Now, I can't seem to get them to respond to me... I've followed up twice now since sending it (once a day) and I'm feeling uncomfortable about having sent it with not a single sort of response, not even a declined for the apartment or any such acknowledgement. Not sure what I should do or if there is anything i can do at this point beside know better to not do it again. any advice?
What you can do now
Many characteristics of houses in the US (I am assuming you live in the US) are a matter of public record. This includes ownership history. These records can can be consulted through the county recorder/county tax assessor's office. Many have a website you can use and offer records dating back to the sixties. I am not sure whether such inquiries come at a fee, but it stands to reason. Example here. You could attempt to validate that the individual you dealt with actually owns the property.
What you could've done
From a technical standpoint, and realizing that most people outside this industry don't care about security of information in transit, a good idea is often to ask to share the information through the same public email service. Ideally this service is a reputable one. Take a look at this previous answer regarding exchanges between gmail accounts:
Make sure to zip your sensitive data with an application that has a respectable implementation of crypto, such as SecureZip and send the password(a reasonably random one) to said zip file through a different channel, like the phone.
Perform the above mentioned validation before the fact.
Realty agencies exist for a good reason. Make sure to conduct business through an experienced and recommended realtor that has a reputation to protect. This will also come to the rescue, should issues or misunderstandings arise during the life of your lease, saving you a lot of time and money.