The "Print to jpeg" option in LR Print module is essentially the same as printing to a printer in that you can still specify:
- File Resolution: typically 360 for Epson printers;
- Print Sharpening: typically Standard unless you know something else is needed for the file being sent;
- Media Type: typically Glossy for everything except true matte paper; and, perhaps most importantly...
- Color Management: Check with your service provider for the colour space and paper profile. If you know what paper they are using, then you can download the profile for that printer.
then "Print to File" and send it to them.