On Sat, August 9, 2008 13:41, Sandy Drobic wrote:
Amedee Van Gasse wrote:
On Sat, August 9, 2008 02:08, Alexey Eremenko wrote:
How about *forcing* email servers to use reverse DNS against all incoming email and the email "From: " field ?
I.e. If I received from someone@opensuse.org, but source IP address cannot be reverse-DNS-resolved, that it really came from openSUSE@org, wuch email can be automatically sent to spam folder. Is this possible ?
What are you talking about? a) Email headers: From: b) SMTP headers: MAIL FROM:
I assume you are talking about the difference between envelope sender and the From: field in the DATA part of the mail.
Yes, you assume right.
Please to not use global sender verification. It is like catching flies with a hammer. You might get some once in a while but the damage you do while using said appliance is rather heavy.
Yes, I agree. That is sort of what I wrote too.
In case of the listserver you would verify the sender address of the listserver (not very useful).
opensuse-de+bounces-32203-suse-linux=japantest.homelinux.com@opensuse.org
In this case I would have to check if the listserver would even recognise the address extension as a valid address. Additionally, a lot of other big companies don't use valid sender addresses, so the false positive rate is rather high.
I know. I work for company number 39 on that well known list, and I'm doing 2nd level email support on one of the sites. We have just done a migration from Notes to Exchange, last year. Now I know there are lots of very good reasons why sometimes it isn't possible to have valid sender addresses. If a company is in a transition phase, you have to live with that.
An additional risk is that some ISPs are blacklisting you if your probes result in too many rejected address probes. T-Online.de for example blacklists you if you try to send to more than 40 invalid recipients within 24 hours.
I didn't know that for sure, but I believe you. It sounds familiar.
Don't use whitelists for sender verification, instead use it only for select domains that are falsified often.
That is what I meant to write but my Engrish is not so good. :-)
You might get away with that if you only use the server for your own needs but once the server is used by many people it's simply not possible to know all desired clients or mails anymore.
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