email subscription repeatedly inactivated for no apparent reason

[xqa]

One of the people who subscribes to one of our feeds via email has not
been receiving it for the last month or so. I checked the
subscription list and he was marked as inactive. I reactivated, but
it reverted to inactive the next day or so. Lather, rinse, repeat--
he's still not getting the email. Tech guys on his end checked his
spam filters, blacklists, etc, and can't find any reason why he's not
getting the message. Now what?

[kovie]

I too have a few subscribers whose emails are going inactive without
highlighting ("Highlighted rows indicate 5 or more unsuccessful
delivery attempts"). I reactivated them before my last post went out
and now they're inactive again after only one post. Is there a way
for subscribers to deactivate their own email address if they want to
take a break?