diff --git a/internal/user/imap.go b/internal/user/imap.go
index 33effdb8..f6257f4b 100644
--- a/internal/user/imap.go
+++ b/internal/user/imap.go
@@ -180,8 +180,14 @@ func (conn *imapConnector) CreateMessage(
 	flags imap.FlagSet,
 	date time.Time,
 ) (imap.Message, []byte, error) {
+	// Compute the hash of the message (to match it against SMTP messages).
+	hash, err := getMessageHash(literal)
+	if err != nil {
+		return imap.Message{}, nil, err
+	}
+
 	// Check if we already tried to send this message recently.
-	if messageID, ok, err := conn.sendHash.hasEntryWait(ctx, literal, time.Now().Add(90*time.Second)); err != nil {
+	if messageID, ok, err := conn.sendHash.hasEntryWait(ctx, hash, time.Now().Add(90*time.Second)); err != nil {
 		return imap.Message{}, nil, fmt.Errorf("failed to check send hash: %w", err)
 	} else if ok {
 		message, err := conn.client.GetMessage(ctx, messageID)
diff --git a/internal/user/send_recorder.go b/internal/user/send_recorder.go
index e214acb6..378ea67e 100644
--- a/internal/user/send_recorder.go
+++ b/internal/user/send_recorder.go
@@ -34,7 +34,6 @@ import (
 const sendEntryExpiry = 30 * time.Minute
 
 type sendRecorder struct {
-	hasher func([]byte) (string, error)
 	expiry time.Duration
 
 	entries     map[string]*sendEntry
@@ -43,7 +42,6 @@ type sendRecorder struct {
 
 func newSendRecorder(expiry time.Duration) *sendRecorder {
 	return &sendRecorder{
-		hasher:  getMessageHash,
 		expiry:  expiry,
 		entries: make(map[string]*sendEntry),
 	}
@@ -58,40 +56,30 @@ type sendEntry struct {
 // tryInsertWait tries to insert the given message into the send recorder.
 // If an entry already exists but it was not sent yet, it waits.
 // It returns whether an entry could be inserted and an error if it times out while waiting.
-func (h *sendRecorder) tryInsertWait(ctx context.Context, b []byte, deadline time.Time) (string, bool, error) {
-	hash, err := h.hasher(b)
-	if err != nil {
-		return "", false, fmt.Errorf("failed to hash message: %w", err)
-	}
-
+func (h *sendRecorder) tryInsertWait(ctx context.Context, hash string, deadline time.Time) (bool, error) {
 	// If we successfully inserted the hash, we can return true.
 	if h.tryInsert(hash) {
-		return hash, true, nil
+		return true, nil
 	}
 
 	// A message with this hash is already being sent; wait for it.
 	_, wasSent, err := h.wait(ctx, hash, deadline)
 	if err != nil {
-		return "", false, fmt.Errorf("failed to wait for message to be sent: %w", err)
+		return false, fmt.Errorf("failed to wait for message to be sent: %w", err)
 	}
 
 	// If the message failed to send, try to insert it again.
 	if !wasSent {
-		return h.tryInsertWait(ctx, b, deadline)
+		return h.tryInsertWait(ctx, hash, deadline)
 	}
 
-	return hash, false, nil
+	return false, nil
 }
 
 // hasEntryWait returns whether the given message already exists in the send recorder.
 // If it does, it waits for its ID to be known, then returns it and true.
 // If no entry exists, or it times out while waiting for its ID to be known, it returns false.
-func (h *sendRecorder) hasEntryWait(ctx context.Context, b []byte, deadline time.Time) (string, bool, error) {
-	hash, err := h.hasher(b)
-	if err != nil {
-		return "", false, fmt.Errorf("failed to hash message: %w", err)
-	}
-
+func (h *sendRecorder) hasEntryWait(ctx context.Context, hash string, deadline time.Time) (string, bool, error) {
 	if !h.hasEntry(hash) {
 		return "", false, nil
 	}
@@ -107,7 +95,7 @@ func (h *sendRecorder) hasEntryWait(ctx context.Context, b []byte, deadline time
 		return messageID, true, nil
 	}
 
-	return h.hasEntryWait(ctx, b, deadline)
+	return h.hasEntryWait(ctx, hash, deadline)
 }
 
 func (h *sendRecorder) tryInsert(hash string) bool {
diff --git a/internal/user/send_recorder_test.go b/internal/user/send_recorder_test.go
index b5f9dea1..ffe291c6 100644
--- a/internal/user/send_recorder_test.go
+++ b/internal/user/send_recorder_test.go
@@ -29,7 +29,7 @@ func TestSendHasher_Insert(t *testing.T) {
 	h := newSendRecorder(sendEntryExpiry)
 
 	// Insert a message into the hasher.
-	hash1, ok, err := h.tryInsertWait(context.Background(), []byte(literal1), time.Now().Add(time.Second))
+	hash1, ok, err := testTryInsert(h, literal1, time.Now().Add(time.Second))
 	require.NoError(t, err)
 	require.True(t, ok)
 	require.NotEmpty(t, hash1)
@@ -38,12 +38,12 @@ func TestSendHasher_Insert(t *testing.T) {
 	h.addMessageID(hash1, "abc")
 
 	// Inserting a message with the same hash should return false.
-	_, ok, err = h.tryInsertWait(context.Background(), []byte(literal1), time.Now().Add(time.Second))
+	_, ok, err = testTryInsert(h, literal1, time.Now().Add(time.Second))
 	require.NoError(t, err)
 	require.False(t, ok)
 
 	// Inserting a message with a different hash should return true.
-	hash2, ok, err := h.tryInsertWait(context.Background(), []byte(literal2), time.Now().Add(time.Second))
+	hash2, ok, err := testTryInsert(h, literal2, time.Now().Add(time.Second))
 	require.NoError(t, err)
 	require.True(t, ok)
 	require.NotEmpty(t, hash2)
@@ -53,7 +53,7 @@ func TestSendHasher_Insert_Expired(t *testing.T) {
 	h := newSendRecorder(time.Second)
 
 	// Insert a message into the hasher.
-	hash1, ok, err := h.tryInsertWait(context.Background(), []byte(literal1), time.Now().Add(time.Second))
+	hash1, ok, err := testTryInsert(h, literal1, time.Now().Add(time.Second))
 	require.NoError(t, err)
 	require.True(t, ok)
 	require.NotEmpty(t, hash1)
@@ -65,7 +65,7 @@ func TestSendHasher_Insert_Expired(t *testing.T) {
 	time.Sleep(time.Second)
 
 	// Inserting a message with the same hash should return true because the previous entry has since expired.
-	hash2, ok, err := h.tryInsertWait(context.Background(), []byte(literal1), time.Now().Add(time.Second))
+	hash2, ok, err := testTryInsert(h, literal1, time.Now().Add(time.Second))
 	require.NoError(t, err)
 	require.True(t, ok)
 
@@ -77,7 +77,7 @@ func TestSendHasher_Wait_SendSuccess(t *testing.T) {
 	h := newSendRecorder(sendEntryExpiry)
 
 	// Insert a message into the hasher.
-	hash, ok, err := h.tryInsertWait(context.Background(), []byte(literal1), time.Now().Add(time.Second))
+	hash, ok, err := testTryInsert(h, literal1, time.Now().Add(time.Second))
 	require.NoError(t, err)
 	require.True(t, ok)
 	require.NotEmpty(t, hash)
@@ -89,7 +89,7 @@ func TestSendHasher_Wait_SendSuccess(t *testing.T) {
 	}()
 
 	// Inserting a message with the same hash should fail.
-	_, ok, err = h.tryInsertWait(context.Background(), []byte(literal1), time.Now().Add(time.Second))
+	_, ok, err = testTryInsert(h, literal1, time.Now().Add(time.Second))
 	require.NoError(t, err)
 	require.False(t, ok)
 }
@@ -98,7 +98,7 @@ func TestSendHasher_Wait_SendFail(t *testing.T) {
 	h := newSendRecorder(sendEntryExpiry)
 
 	// Insert a message into the hasher.
-	hash, ok, err := h.tryInsertWait(context.Background(), []byte(literal1), time.Now().Add(time.Second))
+	hash, ok, err := testTryInsert(h, literal1, time.Now().Add(time.Second))
 	require.NoError(t, err)
 	require.True(t, ok)
 	require.NotEmpty(t, hash)
@@ -110,7 +110,7 @@ func TestSendHasher_Wait_SendFail(t *testing.T) {
 	}()
 
 	// Inserting a message with the same hash should succeed because the first message failed to send.
-	hash2, ok, err := h.tryInsertWait(context.Background(), []byte(literal1), time.Now().Add(time.Second))
+	hash2, ok, err := testTryInsert(h, literal1, time.Now().Add(time.Second))
 	require.NoError(t, err)
 	require.True(t, ok)
 
@@ -122,13 +122,13 @@ func TestSendHasher_Wait_Timeout(t *testing.T) {
 	h := newSendRecorder(sendEntryExpiry)
 
 	// Insert a message into the hasher.
-	hash, ok, err := h.tryInsertWait(context.Background(), []byte(literal1), time.Now().Add(time.Second))
+	hash, ok, err := testTryInsert(h, literal1, time.Now().Add(time.Second))
 	require.NoError(t, err)
 	require.True(t, ok)
 	require.NotEmpty(t, hash)
 
 	// We should fail to insert because the message is not sent within the timeout period.
-	_, _, err = h.tryInsertWait(context.Background(), []byte(literal1), time.Now().Add(time.Second))
+	_, _, err = testTryInsert(h, literal1, time.Now().Add(time.Second))
 	require.Error(t, err)
 }
 
@@ -136,7 +136,7 @@ func TestSendHasher_HasEntry(t *testing.T) {
 	h := newSendRecorder(sendEntryExpiry)
 
 	// Insert a message into the hasher.
-	hash, ok, err := h.tryInsertWait(context.Background(), []byte(literal1), time.Now().Add(time.Second))
+	hash, ok, err := testTryInsert(h, literal1, time.Now().Add(time.Second))
 	require.NoError(t, err)
 	require.True(t, ok)
 	require.NotEmpty(t, hash)
@@ -145,7 +145,7 @@ func TestSendHasher_HasEntry(t *testing.T) {
 	h.addMessageID(hash, "abc")
 
 	// The message was already sent; we should find it in the hasher.
-	messageID, ok, err := h.hasEntryWait(context.Background(), []byte(literal1), time.Now().Add(time.Second))
+	messageID, ok, err := testHasEntry(h, literal1, time.Now().Add(time.Second))
 	require.NoError(t, err)
 	require.True(t, ok)
 	require.Equal(t, "abc", messageID)
@@ -155,7 +155,7 @@ func TestSendHasher_HasEntry_SendSuccess(t *testing.T) {
 	h := newSendRecorder(sendEntryExpiry)
 
 	// Insert a message into the hasher.
-	hash, ok, err := h.tryInsertWait(context.Background(), []byte(literal1), time.Now().Add(time.Second))
+	hash, ok, err := testTryInsert(h, literal1, time.Now().Add(time.Second))
 	require.NoError(t, err)
 	require.True(t, ok)
 	require.NotEmpty(t, hash)
@@ -167,7 +167,7 @@ func TestSendHasher_HasEntry_SendSuccess(t *testing.T) {
 	}()
 
 	// The message was already sent; we should find it in the hasher.
-	messageID, ok, err := h.hasEntryWait(context.Background(), []byte(literal1), time.Now().Add(time.Second))
+	messageID, ok, err := testHasEntry(h, literal1, time.Now().Add(time.Second))
 	require.NoError(t, err)
 	require.True(t, ok)
 	require.Equal(t, "abc", messageID)
@@ -177,7 +177,7 @@ func TestSendHasher_HasEntry_SendFail(t *testing.T) {
 	h := newSendRecorder(sendEntryExpiry)
 
 	// Insert a message into the hasher.
-	hash, ok, err := h.tryInsertWait(context.Background(), []byte(literal1), time.Now().Add(time.Second))
+	hash, ok, err := testTryInsert(h, literal1, time.Now().Add(time.Second))
 	require.NoError(t, err)
 	require.True(t, ok)
 	require.NotEmpty(t, hash)
@@ -189,7 +189,7 @@ func TestSendHasher_HasEntry_SendFail(t *testing.T) {
 	}()
 
 	// The message failed to send; we should not find it in the hasher.
-	_, ok, err = h.hasEntryWait(context.Background(), []byte(literal1), time.Now().Add(time.Second))
+	_, ok, err = testHasEntry(h, literal1, time.Now().Add(time.Second))
 	require.NoError(t, err)
 	require.False(t, ok)
 }
@@ -198,13 +198,13 @@ func TestSendHasher_HasEntry_Timeout(t *testing.T) {
 	h := newSendRecorder(sendEntryExpiry)
 
 	// Insert a message into the hasher.
-	hash, ok, err := h.tryInsertWait(context.Background(), []byte(literal1), time.Now().Add(time.Second))
+	hash, ok, err := testTryInsert(h, literal1, time.Now().Add(time.Second))
 	require.NoError(t, err)
 	require.True(t, ok)
 	require.NotEmpty(t, hash)
 
 	// The message is never sent; we should not find it in the hasher.
-	_, ok, err = h.hasEntryWait(context.Background(), []byte(literal1), time.Now().Add(time.Second))
+	_, ok, err = testHasEntry(h, literal1, time.Now().Add(time.Second))
 	require.NoError(t, err)
 	require.False(t, ok)
 }
@@ -213,7 +213,7 @@ func TestSendHasher_HasEntry_Expired(t *testing.T) {
 	h := newSendRecorder(time.Second)
 
 	// Insert a message into the hasher.
-	hash, ok, err := h.tryInsertWait(context.Background(), []byte(literal1), time.Now().Add(time.Second))
+	hash, ok, err := testTryInsert(h, literal1, time.Now().Add(time.Second))
 	require.NoError(t, err)
 	require.True(t, ok)
 	require.NotEmpty(t, hash)
@@ -225,7 +225,7 @@ func TestSendHasher_HasEntry_Expired(t *testing.T) {
 	time.Sleep(time.Second)
 
 	// The entry has expired; we should not find it in the hasher.
-	_, ok, err = h.hasEntryWait(context.Background(), []byte(literal1), time.Now().Add(time.Second))
+	_, ok, err = testHasEntry(h, literal1, time.Now().Add(time.Second))
 	require.NoError(t, err)
 	require.False(t, ok)
 }
@@ -348,3 +348,26 @@ func TestGetMessageHash(t *testing.T) {
 		})
 	}
 }
+
+func testTryInsert(h *sendRecorder, literal string, deadline time.Time) (string, bool, error) {
+	hash, err := getMessageHash([]byte(literal))
+	if err != nil {
+		return "", false, err
+	}
+
+	ok, err := h.tryInsertWait(context.Background(), hash, deadline)
+	if err != nil {
+		return "", false, err
+	}
+
+	return hash, ok, nil
+}
+
+func testHasEntry(h *sendRecorder, literal string, deadline time.Time) (string, bool, error) {
+	hash, err := getMessageHash([]byte(literal))
+	if err != nil {
+		return "", false, err
+	}
+
+	return h.hasEntryWait(context.Background(), hash, deadline)
+}
diff --git a/internal/user/smtp.go b/internal/user/smtp.go
index 1d27837f..723dfdcf 100644
--- a/internal/user/smtp.go
+++ b/internal/user/smtp.go
@@ -51,14 +51,21 @@ func (user *User) sendMail(authID string, emails []string, from string, to []str
 		return fmt.Errorf("failed to read message: %w", err)
 	}
 
-	// Check if we already tried to send this message recently.
-	hash, ok, err := user.sendHash.tryInsertWait(ctx, b, time.Now().Add(90*time.Second))
+	// Compute the hash of the message (to match it against SMTP messages).
+	hash, err := getMessageHash(b)
 	if err != nil {
+		return err
+	}
+
+	// Check if we already tried to send this message recently.
+	if ok, err := user.sendHash.tryInsertWait(ctx, hash, time.Now().Add(90*time.Second)); err != nil {
 		return fmt.Errorf("failed to check send hash: %w", err)
 	} else if !ok {
 		user.log.Warn("A duplicate message was already sent recently, skipping")
 		return nil
 	}
+
+	// If we fail to send this message, we should remove the hash from the send recorder.
 	defer user.sendHash.removeOnFail(hash)
 
 	// Create a new message parser from the reader.