yes
So if you can use your ISPs webmail (I assume via using a web browser), then go to gmail.com, login to a users gmail acct that you have sent mail to from the SME server, & look in the Spam & other folders. Gmail moves messages to other folders automatically depending on their "type", so either mail from SME server is being identified as spam or identified as some other grouping of email eg Social, & being moved to the applicable folder automatically.
Remember the SME server logs says that gmail accepted the message.