How can I send an e-mail to all webmasters of all sites I've exchanged links with?

Currently LinkMachine does not support sending an e-mail to webmasters of all sites that you've exchanged links with. There are several ways to do this however.

One possibility is to export your link data as a .csv file, under Change Settings, Backup Data. You can then load that .csv file into a spreadsheet program such as Excel. You can sort the sites by status, to isolate only those that you want to send the e-mail to. You can then select the e-mail addresses in Excel of all the sites that you want to send the e-mail to, and copy the addresses into your e-mail client.