questionable email filtering policies?

[chaz at chaz6.com (Chris Hills)]

On 23/07/09 22:22, goemon at anime.net wrote:
> Seems rather unwise to filter your abuse mailbox.
>
> ----- The following addresses had permanent fatal errors -----
> <abuse at btopenworld.com>
> (reason: 554 Message not allowed - UP Email not accepted for policy
> reasons. Please visit
> http://help.yahoo.com/help/us/mail/defer/defer-04.html [120])
>
> -Dan

On the topic of mail rejection I have come across a few sites that 
reject mail, even to postmaster@, from domains that have one or more 
ipv6-only MX records listed (i.e. a domain name with AAAA but no A 
record(s)). The common factor seems to be mimedefang.