I made a habit of sending sending periodic newsletters to my members to keep the board active and remind what’s going on. My members love it, I get a lot of positive feedback. I have 13k + members and I only send to those who has selected "receive e-mail notifications from admin" option in their settings. There is always an option in these e-mail newsletters how to disable notifications for those who prefer not to receive e-mails in the future. Anyway... There are a lot of user accounts whose emails are either not valid, no longer been used or have a full mailbox which causes emails to bounce. I've selected the mails to be send with -f parameter, after that the number of bounced emails decreased but still, 100-200 emails bounces. I really wish there were an option where these accounts could be detected and marked as "awaiting confirmation" so I would no longer send these users newsletters. Is there a way that I’m not aware of to detect these accounts?