Snail Mail is an option to send a hard copy of your estimates/invoices to the shipping address of the your customer. In order to send snail mails to your customer you will need to buy snail mail credits. It is priced at $2/credit.
For sending snail mails to customers in US you will be charged one credit and for the ones in other countries you will charged 2 credits. Snail mails sent to US customers will reach in 5 business days, and will take 10-15 days to reach other countries.
Online accounting software
for small businesses.