[exim] require_verify = sender + RBLs - clarification on the…

Hi All,

I'm trying to understand what would be the impact of enabling:


# require_verify = sender

currently as you can see it is disabled.

I have this code bit in my exim.conf file:


# By default we do NOT require sender verification.
# Sender verification denies unless sender address can be verified:
# If you want to require sender verification, i.e., that the sending
# address is routable and mail can be delivered to it, then
# uncomment the next line. If you do not want to require sender
# verification, leave the line commented out

#require verify = sender

It is almost straighforward to understand what it does, yet I have few questions that I need explicit understanding of:

I have about 190 domains with about 500 mailboxes on my server and as you can understand, every little change affects a great deal
of people.

How would this line affect the usage from my users:

1. Users who will send email via their Outlook/OutlookExpress/Firebird/Mozilla etc.. are already required to enable to "my outgoing server
requires authentication" with their same credentials as their incoming server.

Some of them send emails to other users on the same server and of course to users outside the server.

Those, I believe will not have an issue at all. Am I right?


2. Users who use forms on the server and use localhost and do not use SMTP full credentials, possibly open for exploits and basically
do not provide for a return path, how will they get affected?


3. Users from Outside the server, when they email to a user on the server, does the server check anything with them? is that also being checked?
How exactly? is there a longer, more steps to the handshake?


4. Question number 3, if I understood it correctly, would indicate that I would have dramatically less spam being examined by the RBL checking.
Is that correct?


5. If this is such a good feature, why would it be disabled at onset? What would be a good reason (or perhaps a list of reasons) for disabling this
feature?


Thanks for the clarification.

-Alon.
js@???