PrintBoss is not emailing invoices from one workstation/user
Make certain that Email settings are correctly set in PrintBoss under Options -> Email Settings. In particular, make sure the Email module is enabled (checkbox) and that the server settings are appropriate (check with your IT support, or check the settings for another user where email works) on the SMTP / Mail Hosts tab.
Be sure to check the default addresses tab to set who email comes from and where any copies are sent. If these are left blank, the receiving server may reject the email, or consider it spam.
Also check the Misc. Settings tab to combine several pages of an invoice when printing/emailing and to set any pause required by the SMTP server to avoid spam filters etc.
Finally check the Subject and Message Body tab to change the default email message sent with emails from PrintBoss.