Few days before, one of our users has reported an issue that some of the business experts wanted to use the email functionality for a document library but not able do so as the link is missing or seems to be not visible due to permissions issue!
1. Windows 7 client
2. SharePoint Online / Office 365
I have started my analysis towards the issue and found out that’s it’s a expected behavior. What is meant by expected, refer below for the complete explanation.
Why the option is not there?
The option is not available in Office 365 due to concerns that every document library alias will create a contact in AD, which has some security, performance and traffic related implications.
You can alternatively use Office 365 groups to post attachments (of course email-enabled). The attachments are either distributed to group members via email or kept in OneDrive for Business with a link sent instead.
One more forum from Microsoft’s SharePoint Online:
What it recommends:
Mail-enabled lists are not available with SharePoint Online. Mail-enabled lists create contact objects in AD. Since SharePoint Online is a multi-tenant environment, this functionality would cause a large increase in traffic, which in turn would cause performance issues for all customers.
This functionality is currently disabled due to the performance concerns, as well as security, data requirement, legal compliance and scalability concerns.
Let me know in case of any further queries/questions.