[Exim] yahoo.com makes callout senderverify unusable!?

Hello,

the last days I recognized a lot of frozen bounces
to yahoo.com addresses. I wondered why, because we
are doing a callout, especially for yahoo.com.

So I checked my config using exim -bhc (some foreign IP)
I took a random sender address: 123noop444@???

the result of the callout was

>>> Connecting to mx1.mail.yahoo.com [64.156.215.7]:25 from xxx.xxx.xxx.xxx
... connected
>>> SMTP<< 220 YSmtp mta268.mail.scd.yahoo.com ESMTP service ready
>>> SMTP>> HELO xxxxx
>>> SMTP<< 250 mta268.mail.scd.yahoo.com
>>> SMTP>> MAIL FROM:<>
>>> SMTP<< 250 null sender <> ok
>>> SMTP>> RCPT TO:<123noop444@???>
>>> SMTP<< 250 recipient <123noop444@???> ok
>>> SMTP>> QUIT

first I thought, I have hit an exisiting yahoo.com account,
but sending a non bounce-mail to it ends up with a bounce:

  123noop444@???
    SMTP error from remote mailer after end of data:
    host mx1.mail.yahoo.com [64.157.4.78]: 554 delivery error:
    dd This user doesn't have a yahoo.com account (123noop444@???) [0]
- mta122.mail.sc5.yahoo.com

So what are the yahoo-MTAs doing? Accept every null-sender mail, making
callouts impossible?

Did anyone else recognize this?

I am not amused...

Mit freundlichen Grüßen
Matthias Lewandowski
Systemtechnik Internet


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