We have just started emailing invoices and offering online payment. I import my invoices using iif. To get the information for the iif file, I run a customer report, export it to excel, and then use that to do a mail merge.
I learned last year that I needed a "To Send" field in my TRANS line but I can't find a report that includes "Preferred Send Method." I use a memorized Customer Contact List but that field is not an option and I can't find another report that includes it that I could even export and merge with my current report.