Direct Mail Criteria in todays market

I would like to try a crack at a direct mail campaign. We are trying to locate another investment property in AL. We are pre-approved, as well as have cash in hand for a flip/BRRRR property. However, it has been difficult to find a good property to flip/BRRRR. I have read a few articles and have noticed a few common themes: be consistent, get free information from .gov sites, consider pay services (Listsource, Propstream, etc.), consider absentee owners, pre-delinquent, divorce, probate etc. However, I'm wondering if people still consider this worthwhile and if so, what type of criteria should I focus on for a first time mailing? I plan to pay for a list from List source. Currently, I am interested in finding property to flip/BRRRR 3 bedroom 2 bathroom 1,500-2,500 sqft in the 50-120k range. I'm worried of getting the criteria wrong and spending lots of money sending mailings to the wrong demographic. I have a specific area code that I am looking to buy in as well. For those who have found success with this what criteria do you use? Does COVID-19 change any of your criteria? What paid services do you find the most useful? Finally, if my goal is to get 1-2 deals under contract how many letters should I consider sending? I understand that question is dependent on a number of variables but I'm just looking for a general number. I understand it's a trial and error process but I would just like to be sure I have the bulk of everything right. As always, thanks in advance for any advice on the subject.