Garbage in equals garbage out is the old data tenant that basically means that clean data results in better results for everything. The same applies to the customer mapping feature in 5x5. We've seen all kinds of data over the years, and most of it isn't pristine, so don't worry about how messy your data is as there is a way to clean it.
First off, get the broadest output into an XLSX file from your EPR, CRM or wherever your customer data resides...maybe a bit of both. Once you have this completed, you can go through some simple steps to clean your data.
Using the Advanced Filter feature in Excel (under the DATA tab) you can select cells to scan for duplicates and then remove them or save them to a separate file.
You can also use the same to remove PO Box related addresses, since these will not geo-code for obvious reasons.
And also, there are free and paid services to help you clean your data. Most are very simple to use and result in cleaner files. One to try out is the Experian Data Quality site HERE.
And when you do input your data into 5x5 as we geo-code the customer sites we generate an exception report for any addresses that didn't geo-code. So you can share this report with your team and further clean your original source of data.