How in-app notification and email notification works? How Email invitation can be sent?

You can enable the email notification as explained here110. 

You can enable notification for one group as explained here60. 

Here is the list of events you will receive a notification for185. 

Here is how you can prevent emails from ending up in spam144. 

Here is how you as a user can change the frequency of the email you receive57. 

Here is how you can invite someone to the community65 using an email invitation. 

Here is how you can send a welcome email58. 

Not receiving emails? Check this99. 

Still have a question? Please check this Q&A page.28