BuddyPress.org

@djpaul Does BuddyPress use the same email-address for sending like WordPress? If not, that might be the problem: Some webhosters (like Hosteurope) restrict the usage of email addresses in scripts like WordPress to prevent spam.

For example I usually have to choose one email-address on my webhoster´s config platform. After that I can use it in WordPress. Any other email address won´t work for sending with WordPress, if I don´t use a plugin like https://wordpress.org/plugins/wp-mail-smtp/.