Back in 2020, I wrote this article about using DKIM to sign outgoing mail. This worked well for me for a while: outgoing mail was signed with DKIM and somehow was delivered. Maybe. Who knows.

But now we have a relay server which makes this kind of moot. So I have changed my configuration to use that relay instead of sending email on my own. It seems more reliable that mail seems to be coming from a real machine, so I'm hoping this will have better reputation than my current setup.

In general, you should follow the DSA documentation which includes a Postfix configuration. In my case, it was basically this patch:

diff --git a/postfix/ b/postfix/
index 7fe6dd9e..eabe714a 100644
--- a/postfix/
+++ b/postfix/
@@ -55,3 +55,4 @@ smtp_sasl_security_options =
 smtp_sender_dependent_authentication = yes
 sender_dependent_relayhost_maps = hash:/etc/postfix/sender_relay
 sender_dependent_default_transport_maps = hash:/etc/postfix/sender_transport
+smtp_tls_policy_maps = hash:/etc/postfix/tls_policy
diff --git a/postfix/sender_relay b/postfix/sender_relay
index b486d687..997cce19 100644
--- /dev/null
+++ b/postfix/sender_relay
@@ -0,0 +1,2 @@
+# Per-sender provider; see also /etc/postfix/sasl_passwd.    []:submission
diff --git a/postfix/sender_transport b/postfix/sender_transport
index ca69bc7a..c506c1fc 100644
--- /dev/null
+++ b/postfix/sender_transport
@@ -0,0 +1,1 @@     smtp:
diff --git a/postfix/tls_policy b/postfix/tls_policy
new file mode 100644
index 00000000..9347921a
--- /dev/null
+++ b/postfix/tls_policy
@@ -0,0 +1,1 @@   verify ciphers=high

This configuration differs from the one provided by DSA because I already had the following configured:

sender_dependent_relayhost_maps = hash:/etc/postfix/sender_relay
smtp_sender_dependent_authentication = yes
smtp_sasl_auth_enable = yes
smtp_sasl_password_maps = hash:/etc/postfix/sasl_passwd
smtp_sasl_tls_security_options = noanonymous

I also don't show the patch on /etc/postfix/sasl_passwd for obvious security reasons.

I also had to setup a tls_policy map, because I couldn't use dane for all my remotes. You'll notice I also had to setup a sender_transport because I use a non-default default_transport as well.

It also seems like you can keep the previous DKIM configuration in parallel with this one, as long as you don't double-sign outgoing mail. Since this configuration here is done on my mail client (i.e. not on the server where I am running OpenDKIM), I'm not double-signing so I left the DKIM configuration alone. But if I wanted to remove it, the magic command is:

echo "del dkimPubKey" | gpg --clearsign | mail
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