Buddypress Welcome Email [closed]

For the activation email, you can use the filter hook in buddypress\bp-members\bp-members-functions.php

$message = apply_filters( 'bp_core_signup_send_validation_email_message', $message,    $user_id, $activate_url );

For example, try this in your theme/functions.php

function gavin_welcome_message( $message, $user_id, $activate_url ) {
    $message="Gavin says something here... " . $message;
    return $message; 
}
add_filter('bp_core_signup_send_validation_email_message', 'gavin_welcome_message', 15, 3);