BuddyPress.org

@mrjanvier
if you are using the legacy template
comma separate username will work
For Nouveau, you can use with their mention name with space

@whoam7i7 your request is more specific to 3rd party plugins
for point 1 check with rtMedia as you need to save members avatar inside rtMedia private album and point 2 Capability Manager Enhanced plugin support

@dopeboy You can try https://codex.buddypress.org/themes/bp-custom-php/

@nabeelpommy it will display like this on activity feed if other members keep adding new activities
https://drive.google.com/a/wbcomdesigns.com/file/d/1qH2das7kHKPZ_l2NNNnQpqTJ0sGnQjfU/view?usp=drivesdk
You can try with default 2017 theme

You can find more details here https://buddypress.org/support/topic/sendgrid-and-buddypress-emails/

okay got it, you can add following codes inside
bp-custom.php or child theme functions.php to override
add_filter('bp_email_use_wp_mail', '__return_true');

@mrjanvier on your staging site, try to debug with 2017 theme and deactivate other plugins except BuddyPress to isolate the issue.

@yahven at your site, BuddyPress pages are not mapped
check the following link to setup them

Configure BuddyPress

@farmrchrys2013 Try to debug 2017 theme once, might be theme have some custom codes

Try mailgun, easy to set up and the free plan will be enough.