You fill every field correctly but Zenoss still sayin` that he can`t connect to smtp server?
Here is cheap trick:
Leave fields "SMTP Username" and "SMTP Password blank" and proceed save. You`ll see blank fields are filled again with same entries as before. But there is difference - try send test email and it`s now working.
For some strange reason Zenoss doesn`t save new data entries untill you make that procedure.