I have osclass installed when I registered a user everything worked but when I tried to register another user it didn't send validation email. It sent email to admin that a new user had registered but not to user. I placed a dummy ad through user that it did validate and I manually activated one of the users that didn't get a validation email  and tried sending seller a question and it worked. I have tried registering  2 other users with different email addresses it sent emails to admin but not to users any help appreciated.

Osclass prepare email and give all details to PHP mailer for send.
If some emails are not sent, problem is with mail server.
You may enabled enhanced debug log for PHP mailer to see details:
https://docs.osclasspoint.com/debug-php-errors