I noticed that I've been receiving delivery error e-mails with this error:
'554 delivery error: dd This user doesn't have a yahoo.com account'
but I've also been receiving some e-mails from the e-mail addresses of users who don't have a yahoo.com account according to the delivery errors
So basically I don't know if I should manage the users of which I receive 554 delivery errors or not. Obviously they (or at least part of them, as I've noticed) do have a yahoo.com otherwise they couldn't have e-mailed me.
Has anyone else noticed this? I'm not sure how to deal with this.