There is no way to modify the default text in a retainer invoice email. When sending a retainer invoice, TimeSolve creats an email message ending with the line "It is a pleasure serving you." This sounds like something that belongs at the bottom of restaurant check, not on a lawyer's invoice, but there is currently no way to modify the default email message to delete this text.
How often would you use this request?
Every time we send out a retainer invoice.