Think this worked for me at some stage in the past ... seem to remember gmail itself changed security in the past that may be the problem.
Host set as smtp.gmail.com. Any suggestions ? :(
Double-check the parameters, ports etc.
Switch IMatch to debug logging, check the log file for E> errors and W> warnings it has received from Google's data harvester / gmail.
Thanks Mario ... traced the problem to a setting on Gmail ... see attached file to solution setting in Gmail