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<title>The Exim FAQ Section 8</title>
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<h1>The Exim FAQ</h1>
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<h2><a href="FAQ.html#TOC275">8. REWRITING ADDRESSES</a></h2>
<p>
<a name="TOC276" href="FAQ.html#TOC276">Q0801:</a> How can I get Exim to strip the hostname from the sender's address?
</p>
<p>
<font color="#00BB00">A0801:</font> If you set up a rewriting rule in the following form:
</p>
<pre>
*@*.your.domain $1@your.domain</pre>
<p>
then Exim will rewrite all addresses in the envelope and the headers,
removing anything between <tt>@</tt> and <tt>your.domain</tt>. This applies to all
messages that Exim processes. If you want to rewrite sender addresses
only, the the rule should be
</p>
<pre>
*@*.your.domain $1@your.domain Ffrs</pre>
<p>
This applies the rule only to the envelope sender address and to the
<i>From:</i>, <i>Reply-to:</i>, and <i>Sender:</i> headers.
</p>
<p>
<a name="TOC277" href="FAQ.html#TOC277">Q0802:</a> I have Exim configured to remove the hostname portion of the domain on
outgoing mail, and yet the hostname is present when the mail gets
delivered.
</p>
<p>
<font color="#00BB00">A0802:</font> Check the DNS record for your domain. If the MX record points to a CNAME
record instead of to an A record, some MTAs (not Exim) are liable to
rewrite addresses, changing your domain name to its “canonical” form,
as obtained from the CNAME record.
</p>
<p>
<a name="TOC278" href="FAQ.html#TOC278">Q0803:</a> I want to rewrite local addresses in mail that goes to the outside
world, but not for messages that remain within the local intranet.
</p>
<p>
<font color="#00BB00">A0803:</font> You can use the <tt>headers_rewrite</tt> option on a transport to do this.
The rewriting will then apply to just those copies of a message that
pass through the transport. The <tt>return_path</tt> option can similarly be
used to rewrite the sender address. There is no way of rewriting
recipient addresses at transport time. However, as these are by
definition remote addresses, you probably don't want to rewrite them.
</p>
<p>
You have to set up the configuration so that it uses different SMTP
transports for internal and external mail. If you are using a single
router in both cases, you could configure it like this:
</p>
<pre>
dnslookup:
driver = dnslookup
transport = ${if match{$domain}{\N\.my\.domain$\N}{int_smtp}{ext_smtp}}</pre>
<p>
This example uses the <b>int_smtp</b> transport for domains ending in
<i>.my.domain</i>, and <b>ext_smtp</b> for everything else. The <b>ext_smtp</b> transport
could be something like this:
</p>
<pre>
ext_smtp:
driver = smtp
headers_rewrite = *@*.my.domain \
${lookup{$1}cdb{/etc/$2/mail.handles.cdb}{$value}fail}
return_path = \
${if match{$return_path}{\N^([^@]+)@(.*)\.my\.domain$\N}\
{\
${lookup{$1}cdb{/etc/$2/mail.handles.cdb}{$value}fail}\
}\
fail}</pre>
<p>
This example uses a separate file of local-to-external address
translations for each domain. This is not the only possibility, of
course. The <tt>headers_rewrite</tt> and <tt>return_path</tt> options apply the same
rewriting to the header lines and the envelope sender address,
respectively.
</p>
<p>
<a name="TOC279" href="FAQ.html#TOC279">Q0804:</a> I'm using this rewriting rule to change login names into “friendly”
names, but if mail comes in for an upper case login name, it doesn't
get rewritten.
</p>
<pre>
*@my.domain ${lookup{$1}dbm{/usr/lib/exim/longforms}\
{$value}fail}@my.domain bcfrtFT</pre>
<p>
The longforms database has entries of the form:
</p>
<pre>
ano23: A.N.Other</pre>
<p>
<font color="#00BB00">A0804:</font> Replace <tt>$1</tt> in your rule by <tt>${lc:$1}</tt> to force the local part to lower
case before it is used as a lookup key.
</p>
<p>
<a name="TOC280" href="FAQ.html#TOC280">Q0805:</a> Is it possible to completely fail a message if the rewrite rules fail?
</p>
<p>
<font color="#00BB00">A0805:</font> It depends on what you mean by “fail a message” and what addresses you
are rewriting. If you are rewriting recipient addresses for your local
domain, you can do:
</p>
<pre>
*@dom.ain ${lookup{$1}dbm{/wher/ever}{$value}{failaddr}} Ehq</pre>
<p>
and in your alias file put something like
</p>
<pre>
failaddr: :fail: Rewriting failed</pre>
<p>
This fails a single recipient - others are processed independently.
</p>
<p>
<a name="TOC281" href="FAQ.html#TOC281">Q0806:</a> I'm using <i>$domain</i> as the key for a lookup in a rewriting rule, but its
contents are not being lowercased. Aren't domains supposed to be handled
caselessly?
</p>
<p>
<font color="#00BB00">A0806:</font> The value of <i>$domain</i> is the actual domain that appears in the address.
It could of course be lower cased, but I know that would cause some
unhappiness, because some people have mixed-case domain names which look
silly if the case is changed. Thus, one wants to preserve the case in
rewrites such as
</p>
<pre>
*@*.TheRap.com something@$domain</pre>
<p>
because “therap” doesn't look like two words. I know it seems trivial,
but it is important to some people - especially if by some unfortunate
accident the lowercased word is something indecent.
</p>
<p>
You can trivally force lower casing by means of the <tt>${lc:</tt> operator.
Instead of <tt>$domain</tt> write <tt>${lc:$domain}</tt>.
</p>
<p>
<a name="TOC282" href="FAQ.html#TOC282">Q0807:</a> I want to rewrite local sender addresses depending on the domain of the
recipient.
</p>
<p>
<font color="#00BB00">A0807:</font> In general, this is not possible, because a message may have more than
one recipient and Exim keeps just a single copy of each message. It may
also deliver one copy of a message with several recipient addresses.
You can do an incomplete job by using a regular expression match in a
rewrite rule to test, for example, the contents of the <i>To:</i> header. This
would work except in cases of multiple recipients.
</p>
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