We're neophytes here, having just moved the list over from Yahoo, and
appreciate the help offered here. I expect we'll (I'll) need some
handholding for a while. Personally, my Unix is rusty; the last time I used
much of it was 1995.

This
   ><[log in to unmask]>:
   >Sorry, no mailbox here by that name. (#5.1.1)
turned out to be a server burp at ptd.net. It was coincidental that it
happened today.

The flood of Yahoo errors was not.

Here's how we handled it
------------------------
* We have 60 [log in to unmask] subscribers. We made a list of those who were
already on NOMAIL, then put all Yahoo subscribers on NOMAIL.
* Time passes. Another subscriber here (that would be Jane) told me that
error messages were slowing down for her list.
* We "query listname with nomail for *@yahoo.*"
* We made a mailing list from the results, deleted the names that should
stay on NOMAIL, and divvied up the list. (We are seven.)

This leaves a managable number for each owner to contact. If we get a
reply, we'll set the subscriber's account to MAIL; if not, it'll stay on
NOMAIL.

How Yahoo created this mess
---------------------------
Yahoo has started charging $30 per year for "enhanced" mail services: POP3,
mail forwarding to primary account, and the ability to read mail in a
regular e-mail client instead of on their ad-laden screens. Today was the
day that the charges took effect, so Yahoo dumped anyone who was using the
"enhanced" services and hadn't paid for them. Boom, at once. Since our
default is individual messages, we started getting a flood of bounce
notices--one per super-unpaid Yahoo subscriber per each post to the list.