[PLUG-TALK] Bounced emails

[Denis Heidtmann]

My sister-in-law in Michigan cannot send mail from her @sbcglobal.net
account to my @dslnorthwest.net account because, according to
dslnorthwest.net, the email server, yahoo, does not comply with rfc
2505.  It turns out that sbcglobal (ATT) uses Yahoo; not all
rejections refer to web81002.mail.mud.yahoo.com,  but all go through
yahoo.

dslnorthwest's explanation to me:

The sending mail server, web81002.mail.mud.yahoo.com, does not accept
any connections.  Therefore our mail gateways are unable to perform
the null sender verification where our mail gateways determine if the
sending mail server is actually a mail server.

Sender verify is specified in RFC 2505,
http://www.faqs.org/rfcs/rfc2505.html where it states "MUST NOT refuse
"MAIL From: <>"

A typical bounce message my sister-in-law receives:

Subject: failure notice

Hi. This is the qmail-send program at yahoo.com.
I'm afraid I wasn't able to deliver your message to the following addresses.
This is a permanent error; I've given up. Sorry it didn't work out.

<evdenev at dslnorthwest.net>:
69.64.224.81 does not like recipient.

Remote host said: 550-Callback setup failed while verifying
<xxxxxxx at sbcglobal.net>
550-(result of an earlier callout reused).
550-The initial connection, or a HELO or MAIL FROM:<> command was
550-rejected. Refusing MAIL FROM:<> does not help fight spam, disregards
550-RFC requirements, and stops you from receiving standard bounce
550-messages. This host does not accept mail from domains whose servers
550-refuse bounces.
550 Sender verify failed
Giving up on 69.64.224.81.

A phone call to att yielded nothing but "sorry. try calling yahoo."


Questions:
Why do some servers refuse to comply with 2505?
Why do some providers require compliance, while others do not (gmail,
for example)?
Is it reasonable for dslnorthwest to require compliance?

-Denis