SMTP mailing blocks the form submission

Hello!

I'm stuck with a curious (and certainly chronoforms-newbie!) issue.
I tested a form with an email notification : it seems to work with PHP mail but not with SMTP.
My SMTP params are ok in Joomla settings and work fine with an other compomemt like Foxcontact.

After clicking on Submit, the page simply gets stuck and turns to blank after a while.
I added some screenshots to help : I also tested it with the basic demo form included, assuming I may have made some mistakes in the email settings of the form... which is possible ! :?




Thanks for any advice !