I bought discussion board.
I did signup(register a user) to use board.
it says “Please check your inbox for an activation email – if you don’t see an email from us, please remember to check your spam folder.”
But I didn’t received activation e-mail. even in spam folder.
How to solve this problem?
This is probably because your email provider or client is filtering out the email. You can use a plugin like this, https://en-gb.wordpress.org/plugins/post-smtp/, to help ensure more reliable delivery of emails.