Hi, Pete -
Assuming by sender and recipient you mean the RFC5321.MailFrom and
RFC5321.RcptTo addresses — ie, those in the envelope — then it should be
straightforward. (You can still do it if you mean the RFC5322.From and
RFC5322.To header addresses, but it's a little more complicated.)
You'll want an entry in your *acl_smtp_rcpt* ACL that uses either the *deny* or
*discard* verb: the former issues an SMTP rejection code back to the
sending server when it needs to reject a recipient address; the latter
pretends to accept the recipient address but then silently discards it.
If this is to apply to a single domain name only then it's probably easiest
to use the *domains* and *sender_domains* conditions to match recipient and
sender domains. For example something like this (untested!):
deny
message = Users in domain-a.com can't send messages to domain-a.com
recipients
domains = domain-a.com
sender_domains = domain-a.com
However if you have two or more domains to apply this to then you instead
need to (1) see if the sender domain is one you're interested in and, if it
is, then (2) check if the sender domain matches the recipient domain. For
example something along these (untested!) lines:
# List of domain names whose users can't send to recipients within the same
domain name.
domainlist blocksamedomainusers = domain-a.com : domain-b.com : domain-c.com
*… Then in your acl_smtp_rcpt ACL …*
deny
message = Users in $sender_address_domain can't send messages to $domain
recipients
sender_domains = +blocksamedomainusers
condition = ${if eqi{$sender_address_domain}{$domain}}
This should work for a message someone in domain-a.com sends to a mix of
recipients: some in the same domain and some in others: the addresses in
the same domain will be rejected/discarded, but the message will still go
through to recipients in other domains.
Cheers,
Mike B-)
On 20 March 2017 at 14:57, Peter Leeman <Peter.Leeman@???> wrote:
> Hi All
>
> Is it possible to block an email if both the sender and recipient domain
> are the same?
> Example - sender@???<mailto:sender@domain-a.com> to
> recipient@???<mailto:recipient@domain-a.com>
>
> The reason I am looking to do this is we are going to be using Exim to
> handle incoming/outgoing mail for a domain hosted on Exchange so any mail
> for domain-a.com being emailed from a mailbox on domain-a.com will never
> leave exchange. We still want a sender on domain-a.com to be able to
> email external domains, but want to prevent incoming emails destined for
> domain-a.com appearing as if they are coming from domain-a.com.
>
> The only alternative I can see at this stage is to have two Exim boxes,
> one to handle incoming the other to handle outgoing.
>
> Thanks for any help.
>
> Regards,
>
> Pete.
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