Capabilities/block/quickmail:cansend
From MoodleDocs
If a user has this capability, then s/he can see the Quickmail block in the course and use it to send emails to other users in the same course.
Note: This documentation is for Moodle 2.7. For up-to-date documentation see Capabilities/block/quickmail:cansend.
If a user has this capability, then s/he can see the Quickmail block in the course and use it to send emails to other users in the same course.