The settings for controlling those messages are as follows:
send tl1 welcome messagesend tl2 promotion message
Search for the following customizable text:
/admin/customize/site_texts?q=system_messages.welcome_tl1system_messages.welcome_tl1_user.subject_templatesystem_messages.welcome_tl1_user.text_body_template
/admin/customize/site_texts?q=system_messages.tl2_promotionsystem_messages.tl2_promotion_message.subject_templatesystem_messages.tl2_promotion_message.text_body_template