diff --git a/imap/structure.go b/imap/structure.go
index 3953074a..d7a3996e 100644
--- a/imap/structure.go
+++ b/imap/structure.go
@@ -73,7 +73,11 @@ func structure(section *rfc822.Section, fields *paramList, writer *dualParListWr
 	fields.addString(writer, mimeSubType)
 
 	extWriter := writer.toSingleWriterFrom2nd()
-	fields.addMap(extWriter, mimeParams)
+	if len(mimeParams) == 0 {
+		fields.addString(extWriter, "")
+	} else {
+		fields.addMap(extWriter, mimeParams)
+	}
 	addDispInfo(fields, extWriter, header)
 	fields.addString(extWriter, header.Get("Content-Language")).
 		addString(extWriter, header.Get("Content-Location"))
@@ -92,13 +96,38 @@ func singlePartStructure(section *rfc822.Section, fields *paramList, writer *dua
 		return err
 	}
 
+	featureFlagProvider := unleash.Get()
 	fields.
 		addString(writer, mimeType).
-		addString(writer, mimeSubType).
-		addMap(writer, mimeParams).
+		addString(writer, mimeSubType)
+
+	// Per RFC3501 if `body-field-params` should be NIL if empty
+	if len(mimeParams) == 0 {
+		fields.addString(writer, "")
+	} else {
+		fields.addMap(writer, mimeParams)
+	}
+
+	// Per RFC2045, if Content-Transfer-Encoding is missing, then we should assuume
+	// that the content is `7BIT`.
+	contentTransferEncoding := func() string {
+		value := header.Get("Content-Transfer-Encoding")
+		// if default 7bit behavior is disabled, just return whatever is  in the header.
+		if featureFlagProvider.GetFlagValue(featureflags.ContentTransferEncodingDefault7BitDisabled) {
+			return value
+		}
+
+		if value == "" {
+			value = "7BIT"
+		}
+
+		return value
+	}
+
+	fields.
 		addString(writer, header.Get("Content-Id")).
 		addString(writer, header.Get("Content-Description")).
-		addString(writer, header.Get("Content-Transfer-Encoding")).
+		addString(writer, contentTransferEncoding()).
 		addNumber(writer, len(section.Body()))
 
 	if mimeType == "message" && mimeSubType == "rfc822" {
diff --git a/imap/structure_test.go b/imap/structure_test.go
index c2fe878a..aed5add5 100644
--- a/imap/structure_test.go
+++ b/imap/structure_test.go
@@ -72,7 +72,18 @@ hey there bro
 	require.NoError(t, err)
 	require.NotNil(t, parsed)
 
-	expected := "((\"text\" \"plain\" (\"charset\" \"utf-8\") NIL NIL \"quoted-printable\" 6 2)(\"message\" \"rfc822\" (\"name\" \"ISO-8859-1.eml\") NIL NIL NIL 127 (NIL \"ISO-8859-1\" ((NIL NIL \"random-mail\" \"pm.me\")) ((NIL NIL \"random-mail\" \"pm.me\")) ((NIL NIL \"random-mail\" \"pm.me\")) ((NIL NIL \"random-mail2\" \"pm.me\")) NIL NIL NIL NIL)(\"text\" \"plain\" (\"charset\" \"iso-8859-1\") NIL NIL NIL 14 1) 6) \"mixed\")"
+	expected := "((\"text\" \"plain\" (\"charset\" \"utf-8\") NIL NIL \"quoted-printable\" 6 2)(\"message\" \"rfc822\" (\"name\" \"ISO-8859-1.eml\") NIL NIL \"7BIT\" 127 (NIL \"ISO-8859-1\" ((NIL NIL \"random-mail\" \"pm.me\")) ((NIL NIL \"random-mail\" \"pm.me\")) ((NIL NIL \"random-mail\" \"pm.me\")) ((NIL NIL \"random-mail2\" \"pm.me\")) NIL NIL NIL NIL)(\"text\" \"plain\" (\"charset\" \"iso-8859-1\") NIL NIL \"7BIT\" 14 1) 6) \"mixed\")"
+	require.Equal(t, expected, parsed.Body)
+}
+
+func TestStructureNoContentTypeParams(t *testing.T) {
+	const message = "Content-Type: text/plain\r\nContent-Transfer-Encoding: 7bit\r\n\r\nbody\r\n"
+
+	parsed, err := NewParsedMessage([]byte(message))
+	require.NoError(t, err)
+	require.NotNil(t, parsed)
+
+	expected := "(\"text\" \"plain\" NIL NIL NIL \"7bit\" 6 1)"
 	require.Equal(t, expected, parsed.Body)
 }
 
@@ -182,7 +193,6 @@ func FuzzNewParsedMessage(f *testing.F) {
 	f.Add(inSeed2)
 
 	f.Fuzz(func(t *testing.T, inputData []byte) {
-
 		_, _ = NewParsedMessage(inputData)
 	})
 }
@@ -201,7 +211,7 @@ func TestMaxMIMEStructureDepthExceeded_KillSwitch_Disabled(t *testing.T) {
 	require.ErrorIs(t, err, errorMaximumMIMEStructureDepthExceeded)
 
 	t.Cleanup(func() {
-		unleash.Init(nil)
+		unleash.Init(&unleash.NullFeatureFlagProvider{})
 	})
 }
 
@@ -218,17 +228,6 @@ func TestMaxMIMEStructureDepthExceeded_KillSwitch_Enabled(t *testing.T) {
 	require.NoError(t, err)
 
 	t.Cleanup(func() {
-		unleash.Init(nil)
-	})
-}
-
-func TestMaxMIMEStructureDepthExceeded_NoFFProvider(t *testing.T) {
-	eml, err := os.ReadFile(filepath.Join("testdata", "mime-structure-depth.eml"))
-	require.NoError(t, err)
-	_, err = NewParsedMessage(eml)
-	require.NoError(t, err)
-
-	t.Cleanup(func() {
-		unleash.Init(nil)
+		unleash.Init(&unleash.NullFeatureFlagProvider{})
 	})
 }
diff --git a/internal/unleash/featureflags/flags.go b/internal/unleash/featureflags/flags.go
index 5a0a4e58..e5cfa971 100644
--- a/internal/unleash/featureflags/flags.go
+++ b/internal/unleash/featureflags/flags.go
@@ -1,11 +1,12 @@
 package featureflags
 
 const (
-	CommandWatcherGlobalDisabled              = "InboxBridgeGenericImapOkHeartbeatDisabled"
-	CommandWatcherNonThunderbirdDisabled      = "InboxBridgeGenericImapOkHeartbeatNonThunderbirdDisabled"
-	ConnectionLimiterDisabled                 = "InboxBridgeGluonConnectionLimiterDisabled"
-	ConnectionLimiterDefaultLimitsDisabled    = "InboxBridgeGluonConnectionLimiterDefaultLimitsDisabled"
-	ConnectionCounterConnectionsLimitDisabled = "InboxBridgeGluonRollingCounterConnectionLimitDisabled"
-	MaximumMIMEStructureDepthDisabled         = "InboxBridgeGluonMaximumMimeStructureDepthLimitDisabled"
-	ApplySentryEventsDisabled                 = "InboxDesktopGluonApplySentryEventsDisabled"
+	CommandWatcherGlobalDisabled               = "InboxBridgeGenericImapOkHeartbeatDisabled"
+	CommandWatcherNonThunderbirdDisabled       = "InboxBridgeGenericImapOkHeartbeatNonThunderbirdDisabled"
+	ConnectionLimiterDisabled                  = "InboxBridgeGluonConnectionLimiterDisabled"
+	ConnectionLimiterDefaultLimitsDisabled     = "InboxBridgeGluonConnectionLimiterDefaultLimitsDisabled"
+	ConnectionCounterConnectionsLimitDisabled  = "InboxBridgeGluonRollingCounterConnectionLimitDisabled"
+	MaximumMIMEStructureDepthDisabled          = "InboxBridgeGluonMaximumMimeStructureDepthLimitDisabled"
+	ApplySentryEventsDisabled                  = "InboxDesktopGluonApplySentryEventsDisabled"
+	ContentTransferEncodingDefault7BitDisabled = "InboxDesktopGluonNoContentTransferEncoding7BitDefaultDisabled"
 )
diff --git a/internal/unleash/singleton.go b/internal/unleash/singleton.go
index ffec7999..80efd8f1 100644
--- a/internal/unleash/singleton.go
+++ b/internal/unleash/singleton.go
@@ -22,5 +22,9 @@ func Init(provider FeatureFlagValueProvider) {
 }
 
 func Get() FeatureFlagValueProvider {
+	if testing.Testing() && instance == nil {
+		instance = &NullFeatureFlagProvider{}
+		return instance
+	}
 	return instance
 }
diff --git a/tests/helper_test.go b/tests/helper_test.go
index 776c5dc0..359f4901 100644
--- a/tests/helper_test.go
+++ b/tests/helper_test.go
@@ -880,6 +880,17 @@ func newEmptyBodyStructureValidator() *bodyStructureValidator {
 		require.Empty(tb, s)
 	}
 
+	validEncoding := func(tb testing.TB, s string) {
+		validValues := []string{"7BIT", "8BIT", "BINARY", "BASE64", "QUOTED-PRINTABLE", ""}
+		tb.Helper()
+		for _, value := range validValues {
+			if strings.EqualFold(value, s) {
+				return
+			}
+		}
+		require.Failf(tb, "string not in allowed values", "got %q, want one of %v", s, validValues)
+	}
+
 	return &bodyStructureValidator{
 		validateMIMEType:    emptyString,
 		validateMimeSubType: emptyString,
@@ -888,7 +899,7 @@ func newEmptyBodyStructureValidator() *bodyStructureValidator {
 		},
 		validateID:          emptyString,
 		validateDescription: emptyString,
-		validateEncoding:    emptyString,
+		validateEncoding:    validEncoding,
 		validateSize: func(tb testing.TB, u uint32) {
 			require.Zero(tb, u)
 		},