Problem receiving spam with invalid "FROM"

[mickier]

I'm seeing a bunch of email with nothing in the FROM: field, just a yahoo "reply-to" field. These messages are received by my server, have an invalid "TO" field, so my server sends a bounce message to the "reply-to" field...

As a result, I'm getting on yahoo's "blacklist" for sending junk to them!

Is there any way to simply block messages which have an invalid "FROM" field? or is this something I wouldn't want to do? Is there a better way to resolve this?

Why should my zimbra server be accepting email with an invalid FROM: field anyway? (although there's probably no sanity or reliability tests done on the from field anyway..)

Basically as far as I can tell, someone is using this as a denial of service attack against me to get block me with yahoo...?

Suggestions?

Thanks in advance!

[phoenix]

You eed to update your forum profile with the output of the following command (do not post the output in this thread):

zmcontrol -v

This might just be NDR spam, you should post some details on what additional techniques you use to block spam (ones from the Zimbra wiki, for example). You should also post some details of the headers from a spam email, do these messages also get into a users mailbox or what?.