while sending new email some contacts cause error: invalid recipient format
Hello Robert, can you please make a screenshot of the error or submit more detailed information about the error from the log in Operations? Copy the content of the log or make a screenshot and submit it to us here on forum for more information about this issue.
What version of eM Client are you currently using on your computer, can you please check the exact release number in Help > About? What mail service are you using with eM Client?
Regards,