It works for me at my domain for an email from the same domain. I have not tried with google accounts, but there can be some common issues when you have failed attempts
The mail account valid by connecting it through Outlook / Thunderbird.
If not, check timeout. Add following code added to modules/MailManager/models/Mailbox.php (line128) $refreshTimeout = ($this->refreshTimeOut()!='')?$this->refreshTimeOut():0;// to fix the empty refresh time issue
Set correct TLS/SSL/NoTLS options as per your mail account