Click "Participants" from the course administration tab.

To add additional filters, click "Add condition".

Click "Select" to apply filters as desired. This example will show how to send an email to a specific group.

Select
Keyword
Status
Roles
Enrolment methods
Groups
Inactive for more than
Country

After selecting "group" filter. in the next dropdown menu selecting "Group A" will select that particular group.

Additional filters can be selected if necessary by clicking "Add condition".

Match 
None
Any
All
 of the following:
Filter 1
Match
None
Any
All
Filter type
Select
Keyword
Status
Roles
Enrolment methods
Groups
Inactive for more than
Country
Status
▼
 
Selected items:
Active
AND
Filter 2
Match
None
Any
All
Filter type
Select
Keyword
Status
Roles
Enrolment methods
Groups
Inactive for more than
Country
Groups
▼
 
Selected items:
Group A
 
Add condition
Clear filters
Apply filters

Filters can be removed by clicking the cross.

Click "Apply filters" to update the participants list.

Click the 'Select all' field to select all students from the current page.

For multiple pages of students, use the "Select all..." button at the bottom of the page. 

After selecting all desired participants,  select an option from the  dropdown menu what to do with the selected users.

Choose...
Send a message
Add a new note
Comma separated values (.csv)
Microsoft Excel (.xlsx)
HTML table
Javascript Object Notation (.json)
OpenDocument (.ods)
Portable Document Format (.pdf)
Send an email (comma separator)
Send an email (semi-colon separator)
Download as CSV

Select "Send an email (comma separator)" or "Send an email (semi-colon separator)". 

Your default email application will open a new blank email, with your own email address in the "To" field. All the recipients you chose will be listed in the BCC field. Compose and send your message as normal.

Filtering Participants