On Thu, 2009-04-23 at 12:22 -0400, jean-paul natola wrote:
> Exchange has the option to reject messages for non-existant users i.e.
> invalid_user@??? , if I enable this feature, what will exim
> do with thius type of message?
>
As things stand, and you turn this on (which you should!), Exim will
generate a bounce message when it tries to deliver the message to the
invalid recipient. However...
> is it going to crash my exim? is this safe to enable?
No it won't, and yes it is.
This is one of the rare times when the use of recipient verification
callouts is perfectly acceptable. Use something like this at an
appropriate point in your RCPT ACL:
deny domains = +relay_to_domains
!verify =
recipient/callout=30s,defer_ok,no_cache,use_sender/no_details
log_message = RCPT VERIFY RETURNED: $acl_verify_message
The required options will vary according to your local setup - the
domain list will need changing, for example, and you may want to tune
the cache and defer settings.
What that will do is call forward to the Exchange server handling
example com when a remote site says "RCPT TO: invalid_user@???",
and accept or reject the command based on the response the Exchange
server gives.
Note that this doesn't scale well into very large environments, where
you should be keeping a list of valid recipients in some other form (for
example using LDAP lookups against your Active Directory).
Graeme
