diff --git a/CHANGELOG.md b/CHANGELOG.md
index 4f1f689..54d396b 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,5 +1,10 @@
 # SpamAssassin Milter changelog
 
+## unreleased
+
+*   Add `--reply-text` option to allow customising the reply text when rejecting
+    spam.
+
 ## 0.1.2 (2020-06-07)
 
 *   Bump milter dependency to version 0.2.1.
diff --git a/spamassassin-milter.8 b/spamassassin-milter.8
index 738a415..a2f02b7 100644
--- a/spamassassin-milter.8
+++ b/spamassassin-milter.8
@@ -7,6 +7,7 @@ spamassassin-milter \- milter for spam filtering with SpamAssassin
 .RB [ \-B ]
 .RB [ \-H ]
 .RB [ \-n ]
+[\fB\-R\fR \fIMSG\fR]
 .RB [ \-r ]
 [\fB\-s\fR \fIBYTES\fR]
 [\fB\-t\fR \fINETS\fR]
@@ -114,6 +115,12 @@ Reject messages flagged as spam at the SMTP level.
 Rejection results in a permanent SMTP error being returned to the client, and
 the message is not delivered.
 .TP
+.BR \-R ", " \-\-reply-text " \fIMSG\fR"
+Reply with SMTP reply text
+.I MSG
+when rejecting a message flagged as spam.
+For multiline replies, use an ASCII newline character as the line separator.
+.TP
 .BR \-t ", " \-\-trusted-networks " \fINETS\fR"
 Trust connections coming from the IP networks or addresses
 .IR NETS .
diff --git a/src/client.rs b/src/client.rs
index 23d041d..5a5ceb3 100644
--- a/src/client.rs
+++ b/src/client.rs
@@ -266,8 +266,8 @@ fn reject_spam(id: &str, actions: &impl SetErrorReply, config: &Config) -> milte
         Status::Accept
     } else {
         // These reply codes are the most appropriate according to RFCs 5321 and
-        // 3463. The text is kept generic and makes no mention of SpamAssassin.
-        actions.set_error_reply("550", Some("5.7.1"), vec!["Spam message refused"])?;
+        // 3463. The default text is generic and does not mention SpamAssassin.
+        actions.set_error_reply("550", Some("5.7.1"), config.reply_text().lines().collect())?;
 
         verbose!(config, "{}: rejected message flagged as spam", id);
         Status::Reject
diff --git a/src/config.rs b/src/config.rs
index 22fba02..426a105 100644
--- a/src/config.rs
+++ b/src/config.rs
@@ -13,6 +13,7 @@ pub struct ConfigBuilder {
     max_message_size: usize,
     dry_run: bool,
     reject_spam: bool,
+    reply_text: String,
     preserve_headers: bool,
     preserve_body: bool,
     verbose: bool,
@@ -64,6 +65,11 @@ impl ConfigBuilder {
         self
     }
 
+    pub fn reply_text(&mut self, value: String) -> &mut Self {
+        self.reply_text = value;
+        self
+    }
+
     pub fn preserve_headers(&mut self, value: bool) -> &mut Self {
         self.preserve_headers = value;
         self
@@ -94,6 +100,7 @@ impl ConfigBuilder {
             max_message_size: self.max_message_size,
             dry_run: self.dry_run,
             reject_spam: self.reject_spam,
+            reply_text: self.reply_text,
             preserve_headers: self.preserve_headers,
             preserve_body: self.preserve_body,
             verbose: self.verbose,
@@ -112,6 +119,8 @@ impl Default for ConfigBuilder {
             max_message_size: 512_000,  // same as in `spamc`
             dry_run: Default::default(),
             reject_spam: Default::default(),
+            // Generic default reply text that makes no mention of SpamAssassin.
+            reply_text: String::from("Spam message refused"),
             preserve_headers: Default::default(),
             preserve_body: Default::default(),
             verbose: Default::default(),
@@ -130,6 +139,7 @@ pub struct Config {
     max_message_size: usize,
     dry_run: bool,
     reject_spam: bool,
+    reply_text: String,
     preserve_headers: bool,
     preserve_body: bool,
     verbose: bool,
@@ -172,6 +182,10 @@ impl Config {
         self.reject_spam
     }
 
+    pub fn reply_text(&self) -> &str {
+        &self.reply_text
+    }
+
     pub fn preserve_headers(&self) -> bool {
         self.preserve_headers
     }
diff --git a/src/main.rs b/src/main.rs
index d03719a..9397088 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -9,6 +9,7 @@ const ARG_MILTER_DEBUG_LEVEL: &str = "MILTER_DEBUG_LEVEL";
 const ARG_PRESERVE_BODY: &str = "PRESERVE_BODY";
 const ARG_PRESERVE_HEADERS: &str = "PRESERVE_HEADERS";
 const ARG_REJECT_SPAM: &str = "REJECT_SPAM";
+const ARG_REPLY_TEXT: &str = "REPLY_TEXT";
 const ARG_TRUSTED_NETWORKS: &str = "TRUSTED_NETWORKS";
 const ARG_VERBOSE: &str = "VERBOSE";
 const ARG_SOCKET: &str = "SOCKET";
@@ -52,6 +53,12 @@ fn main() {
             .long("reject-spam")
             .conflicts_with_all(&[ARG_PRESERVE_BODY, ARG_PRESERVE_HEADERS])
             .help("Reject messages flagged as spam"))
+        .arg(Arg::with_name(ARG_REPLY_TEXT)
+            .short("R")
+            .long("reply-text")
+            .value_name("MSG")
+            .requires(ARG_REJECT_SPAM)
+            .help("Reply text when rejecting messages"))
         .arg(Arg::with_name(ARG_TRUSTED_NETWORKS)
             .short("t")
             .long("trusted-networks")
@@ -147,6 +154,10 @@ fn build_config(matches: &ArgMatches<'_>) -> Result<Config> {
         config.verbose(true);
     }
 
+    if let Some(msg) = matches.value_of(ARG_REPLY_TEXT) {
+        config.reply_text(msg.to_owned());
+    }
+
     if let Some(level) = matches.value_of(ARG_MILTER_DEBUG_LEVEL) {
         config.milter_debug_level(level.parse().unwrap());
     }
diff --git a/tests/reject_spam.lua b/tests/reject_spam.lua
index cf3bf85..62c22b5 100644
--- a/tests/reject_spam.lua
+++ b/tests/reject_spam.lua
@@ -63,7 +63,7 @@ local err = mt.eom(conn)
 assert(err == nil, err)
 assert(mt.getreply(conn) == SMFIR_REPLYCODE)
 
-assert(mt.eom_check(conn, MT_SMTPREPLY, "550", "5.7.1", "Spam message refused"))
+assert(mt.eom_check(conn, MT_SMTPREPLY, "550", "5.7.1", "Not allowed!"))
 
 local err = mt.disconnect(conn)
 assert(err == nil, err)
diff --git a/tests/reject_spam.rs b/tests/reject_spam.rs
index 0e3412a..809e805 100644
--- a/tests/reject_spam.rs
+++ b/tests/reject_spam.rs
@@ -6,8 +6,10 @@ use spamassassin_milter::*;
 #[test]
 fn reject_spam() {
     let mut builder = Config::builder();
-    builder.reject_spam(true);
-    builder.spamc_args(vec![format!("--port={}", SPAMD_PORT)]);
+    builder
+        .reject_spam(true)
+        .reply_text("Not allowed!".into())
+        .spamc_args(vec![format!("--port={}", SPAMD_PORT)]);
     let config = builder.build();
 
     let server = spawn_mock_spamd_server(SPAMD_PORT, |spam| {