Hey Paul Gibbs, I did what you asked and the results in the mail i got from the site admin was :
Email delivered – true
Also i do get mails when users change stuff from there wordpress profile, for example in the backand i changed a users email and he got a mail of email change.
My users do not get any mails from registering or activitys on the site they signed up for
Im running into the same problem, But its not just the Activation mails, its any kind of mail related to buddypress thats not working anymore. My members get no updates and cant activate. Please Bring us a fix/solution Asap