Might be a good time to mention a new development with Yahoo Mail. They now appear to use a form of shadow ban. They will accept an email, with all outward sym

Might be a good time to mention a new development with Yahoo Mail. They now appear to use a form of shadow ban. They will accept an email, with all outward symptoms being normal, but it will not appear anywhere in the user's mailbox. Not even in the Spam folder. This started few months ago when we were sending out our (rather infrequent) newsletter. 5th or so message to ...@yahoo.com address failed with 421 4.7.0 [TSS04] Messages from xx.xx.xx.xx temporarily deferred due to user complaints - 4.16.55.1; see https://help.yahoo.com/kb/postmaster/SLN3434.html (in reply to MAIL FROM command) That's with just a couple of seconds in. They kept replying with 421 for a while, but later switched to just dropping connections. Then, in the course of the next few days, they would accept 1-2 emails and then go back to denying them again. As I mentioned above, the "best" part is that none of these emails would actually make it into recipient's mailboxes. They disappear. Better yet, all subsequent (non-bulk) emails have the same fate as do _replies_ to emails from Ymail users. This last bit is what makes this look like a shadow ban. All attempts to contact Yahoo went unanswered, including those made through Gmail. Ditto for whitelisting requests through their web form. If anyone has any ideas what the hell's going on, I'd be curious to hear them.