diff --git a/mirai-core-qqandroid/src/commonMain/kotlin/net/mamoe/mirai/qqandroid/QQAndroidBot.common.kt b/mirai-core-qqandroid/src/commonMain/kotlin/net/mamoe/mirai/qqandroid/QQAndroidBot.common.kt
index 5a0b3fdae..e8f94beeb 100644
--- a/mirai-core-qqandroid/src/commonMain/kotlin/net/mamoe/mirai/qqandroid/QQAndroidBot.common.kt
+++ b/mirai-core-qqandroid/src/commonMain/kotlin/net/mamoe/mirai/qqandroid/QQAndroidBot.common.kt
@@ -182,11 +182,11 @@ internal abstract class QQAndroidBotBase constructor(
     }
 
     @Suppress("RemoveExplicitTypeArguments") // false positive
-    @ExperimentalMessageSource
     override suspend fun recall(source: MessageSource) {
         // println(source._miraiContentToString())
 
         check(source is MessageSourceImpl)
+        source.ensureSequenceIdAvailable()
 
         val response: PbMessageSvc.PbMsgWithDraw.Response = when (source) {
             is MessageSourceToGroupImpl,
@@ -216,6 +216,7 @@ internal abstract class QQAndroidBotBase constructor(
                     ).sendAndExpect<PbMessageSvc.PbMsgWithDraw.Response>()
                 }
             }
+            is OfflineMessageSource,
             is MessageSourceFromFriendImpl,
             is MessageSourceToFriendImpl
             -> network.run {
@@ -227,7 +228,7 @@ internal abstract class QQAndroidBotBase constructor(
                     source.time
                 ).sendAndExpect<PbMessageSvc.PbMsgWithDraw.Response>()
             }
-            else -> error("stub")
+            else -> error("stub!")
         }
 
         check(response is PbMessageSvc.PbMsgWithDraw.Response.Success) { "Failed to recall message #${source.id}: $response" }
diff --git a/mirai-core-qqandroid/src/commonMain/kotlin/net/mamoe/mirai/qqandroid/utils/type.kt b/mirai-core-qqandroid/src/commonMain/kotlin/net/mamoe/mirai/qqandroid/utils/type.kt
index 64ef2a90f..49d023f10 100644
--- a/mirai-core-qqandroid/src/commonMain/kotlin/net/mamoe/mirai/qqandroid/utils/type.kt
+++ b/mirai-core-qqandroid/src/commonMain/kotlin/net/mamoe/mirai/qqandroid/utils/type.kt
@@ -12,8 +12,6 @@
 
 package net.mamoe.mirai.qqandroid.utils
 
-import net.mamoe.mirai.message.data.*
-import net.mamoe.mirai.message.data.AtAll.display
 import kotlin.jvm.JvmMultifileClass
 import kotlin.jvm.JvmName
 
@@ -32,6 +30,7 @@ internal fun Int.toIpV4AddressString(): String {
     }
 }
 
+/*
 internal fun String.chineseLength(upTo: Int): Int {
     return this.sumUpTo(upTo) { if (it in '\u0391'..'\uFFE5') 3 else 1 }
 }
@@ -41,11 +40,10 @@ internal fun MessageChain.estimateLength(upTo: Int = Int.MAX_VALUE): Int =
         it.estimateLength(up)
     }
 
-@OptIn(ExperimentalMessageSource::class)
 internal fun SingleMessage.estimateLength(upTo: Int = Int.MAX_VALUE): Int {
     return when (this) {
         is QuoteReply -> {
-            700 + source.originalMessage.estimateLength(upTo)
+            700
         }
         // is Image -> 300
         is PlainText -> stringValue.chineseLength(upTo)
@@ -76,3 +74,4 @@ internal inline fun CharSequence.sumUpTo(upTo: Int, selector: (Char) -> Int): In
     }
     return sum
 }
+*/
\ No newline at end of file
diff --git a/mirai-core/src/androidMain/kotlin/net/mamoe/mirai/BotJavaFriendlyAPI.kt b/mirai-core/src/androidMain/kotlin/net/mamoe/mirai/BotJavaFriendlyAPI.kt
index bdbb0a9a1..5e0d51757 100644
--- a/mirai-core/src/androidMain/kotlin/net/mamoe/mirai/BotJavaFriendlyAPI.kt
+++ b/mirai-core/src/androidMain/kotlin/net/mamoe/mirai/BotJavaFriendlyAPI.kt
@@ -5,7 +5,6 @@ import net.mamoe.mirai.contact.PermissionDeniedException
 import net.mamoe.mirai.contact.recall
 import net.mamoe.mirai.data.AddFriendResult
 import net.mamoe.mirai.message.MessageReceipt
-import net.mamoe.mirai.message.data.ExperimentalMessageSource
 import net.mamoe.mirai.message.data.Image
 import net.mamoe.mirai.message.data.MessageChain
 import net.mamoe.mirai.message.data.MessageSource
@@ -62,7 +61,6 @@ actual abstract class BotJavaFriendlyAPI actual constructor() {
      *
      * @see Bot.recall (扩展函数) 接受参数 [MessageChain]
      */
-    @ExperimentalMessageSource
     @JvmName("recall")
     fun __recallBlockingForJava__(source: MessageSource) {
         runBlocking { recall(source) }
@@ -90,7 +88,6 @@ actual abstract class BotJavaFriendlyAPI actual constructor() {
      * @param millis 延迟的时间, 单位为毫秒
      * @see recall
      */
-    @ExperimentalMessageSource
     @JvmName("recallIn")
     fun __recallIn_MemberForJava__(source: MessageSource, millis: Long) {
         runBlocking { recallIn(source, millis) }
@@ -151,7 +148,6 @@ actual abstract class BotJavaFriendlyAPI actual constructor() {
     /**
      * 异步调用 [__recallBlockingForJava__]
      */
-    @ExperimentalMessageSource
     @JvmName("recallAsync")
     fun __recallAsyncForJava__(source: MessageSource): Future<Unit> {
         return future { recall(source) }
diff --git a/mirai-core/src/androidMain/kotlin/net/mamoe/mirai/message/MessageReceipt.kt b/mirai-core/src/androidMain/kotlin/net/mamoe/mirai/message/MessageReceipt.kt
index e2b75c1f8..ebf631b1e 100644
--- a/mirai-core/src/androidMain/kotlin/net/mamoe/mirai/message/MessageReceipt.kt
+++ b/mirai-core/src/androidMain/kotlin/net/mamoe/mirai/message/MessageReceipt.kt
@@ -11,7 +11,6 @@ import net.mamoe.mirai.contact.Contact
 import net.mamoe.mirai.contact.Group
 import net.mamoe.mirai.contact.Member
 import net.mamoe.mirai.contact.QQ
-import net.mamoe.mirai.message.data.ExperimentalMessageSource
 import net.mamoe.mirai.message.data.Message
 import net.mamoe.mirai.message.data.OnlineMessageSource
 import net.mamoe.mirai.message.data.QuoteReply
@@ -24,16 +23,18 @@ import net.mamoe.mirai.utils.unsafeWeakRef
  *
  * 此对象持有 [Contact] 的弱引用, [Bot] 离线后将会释放引用, 届时 [target] 将无法访问.
  *
+ * @param source 指代发送出去的消息
+ * @param target 消息发送对象
+ *
  * @see Group.sendMessage 发送群消息, 返回回执（此对象）
  * @see QQ.sendMessage 发送群消息, 返回回执（此对象）
  *
  * @see MessageReceipt.sourceId 源 id
- * @see MessageReceipt.sourceSequenceId 源序列号
  * @see MessageReceipt.sourceTime 源时间
  */
 @Suppress("FunctionName")
 @OptIn(MiraiInternalAPI::class)
-actual open class MessageReceipt<out C : Contact> @OptIn(ExperimentalMessageSource::class)
+actual open class MessageReceipt<out C : Contact>
 actual constructor(
     actual val source: OnlineMessageSource.Outgoing,
     target: C,
diff --git a/mirai-core/src/commonMain/kotlin/net.mamoe.mirai/event/events/BotEvents.kt b/mirai-core/src/commonMain/kotlin/net.mamoe.mirai/event/events/BotEvents.kt
index 92de5b796..82e751b6c 100644
--- a/mirai-core/src/commonMain/kotlin/net.mamoe.mirai/event/events/BotEvents.kt
+++ b/mirai-core/src/commonMain/kotlin/net.mamoe.mirai/event/events/BotEvents.kt
@@ -18,7 +18,6 @@ import net.mamoe.mirai.event.BroadcastControllable
 import net.mamoe.mirai.event.CancellableEvent
 import net.mamoe.mirai.event.events.ImageUploadEvent.Failed
 import net.mamoe.mirai.event.events.ImageUploadEvent.Succeed
-import net.mamoe.mirai.message.data.ExperimentalMessageSource
 import net.mamoe.mirai.message.data.Image
 import net.mamoe.mirai.message.data.MessageChain
 import net.mamoe.mirai.message.data.MessageSource
@@ -98,7 +97,6 @@ sealed class MessageSendEvent : BotEvent, BotActiveEvent, AbstractCancellableEve
 /**
  * 消息撤回事件. 可是任意消息被任意人撤回.
  */
-@OptIn(ExperimentalMessageSource::class)
 sealed class MessageRecallEvent : BotEvent {
     /**
      * 消息原发送人
diff --git a/mirai-core/src/commonMain/kotlin/net.mamoe.mirai/message/MessageReceipt.kt b/mirai-core/src/commonMain/kotlin/net.mamoe.mirai/message/MessageReceipt.kt
index b0d975c1d..61c5c5846 100644
--- a/mirai-core/src/commonMain/kotlin/net.mamoe.mirai/message/MessageReceipt.kt
+++ b/mirai-core/src/commonMain/kotlin/net.mamoe.mirai/message/MessageReceipt.kt
@@ -34,7 +34,7 @@ import kotlin.jvm.JvmSynthetic
  * @see MessageReceipt.sourceId 源 id
  * @see MessageReceipt.sourceTime 源时间
  */
-expect open class MessageReceipt<out C : Contact> @OptIn(ExperimentalMessageSource::class) constructor(
+expect open class MessageReceipt<out C : Contact>(
     source: OnlineMessageSource.Outgoing,
     target: C,
     botAsMember: Member?
diff --git a/mirai-core/src/commonMain/kotlin/net.mamoe.mirai/message/data/Message.kt b/mirai-core/src/commonMain/kotlin/net.mamoe.mirai/message/data/Message.kt
index 063420a62..dc5bf6cdd 100644
--- a/mirai-core/src/commonMain/kotlin/net.mamoe.mirai/message/data/Message.kt
+++ b/mirai-core/src/commonMain/kotlin/net.mamoe.mirai/message/data/Message.kt
@@ -69,7 +69,7 @@ interface Message {
      *
      * @param M 指代持有这个 Key 的消息类型
      */
-    interface Key<M : Message>
+    interface Key<out M : Message>
 
     infix fun eq(other: Message): Boolean = this.toString() == other.toString()
 
diff --git a/mirai-core/src/commonMain/kotlin/net.mamoe.mirai/message/data/MessageChain.kt b/mirai-core/src/commonMain/kotlin/net.mamoe.mirai/message/data/MessageChain.kt
index c6f47d73b..e48a29af1 100644
--- a/mirai-core/src/commonMain/kotlin/net.mamoe.mirai/message/data/MessageChain.kt
+++ b/mirai-core/src/commonMain/kotlin/net.mamoe.mirai/message/data/MessageChain.kt
@@ -132,7 +132,7 @@ inline fun <reified M : Message> MessageChain.any(): Boolean = this.any { it is
 /**
  * 获取第一个 [M] 类型的 [Message] 实例
  */
-@OptIn(ExperimentalMessageSource::class, MiraiExperimentalAPI::class)
+@OptIn(MiraiExperimentalAPI::class)
 @JvmSynthetic
 @Suppress("UNCHECKED_CAST")
 fun <M : Message> MessageChain.firstOrNull(key: Message.Key<M>): M? = when (key) {
diff --git a/mirai-core/src/commonMain/kotlin/net.mamoe.mirai/message/data/MessageSource.kt b/mirai-core/src/commonMain/kotlin/net.mamoe.mirai/message/data/MessageSource.kt
index 7da76914e..c884707de 100644
--- a/mirai-core/src/commonMain/kotlin/net.mamoe.mirai/message/data/MessageSource.kt
+++ b/mirai-core/src/commonMain/kotlin/net.mamoe.mirai/message/data/MessageSource.kt
@@ -28,12 +28,6 @@ import kotlin.jvm.JvmMultifileClass
 import kotlin.jvm.JvmName
 import kotlin.jvm.JvmSynthetic
 
-/**
- * MessageSource 正计划于 0.32 或 0.33 或之后进行 API 不兼容的重写.
- */
-@RequiresOptIn(message = "MessageSource 正计划于 0.32 或 0.33 或之后进行 API 不兼容的重写", level = RequiresOptIn.Level.WARNING)
-annotation class ExperimentalMessageSource
-
 /**
  * 消息源, 它存在于 [MessageChain] 中, 用于表示这个消息的来源.
  *
@@ -103,6 +97,8 @@ sealed class MessageSource : Message, MessageMetadata {
  */
 @SinceMirai("0.33.0")
 sealed class OnlineMessageSource : MessageSource() {
+    companion object Key : Message.Key<OnlineMessageSource>
+
     /**
      * 消息发送人. 可能为 [机器人][Bot] 或 [好友][QQ] 或 [群员][Member].
      * 即类型必定为 [Bot], [QQ] 或 [Member]
@@ -125,6 +121,8 @@ sealed class OnlineMessageSource : MessageSource() {
      * 由 [机器人主动发送消息][Contact.sendMessage] 产生的 [MessageSource]
      */
     sealed class Outgoing : OnlineMessageSource() {
+        companion object Key : Message.Key<Outgoing>
+
         abstract override val sender: Bot
         abstract override val target: Contact
 
@@ -132,12 +130,16 @@ sealed class OnlineMessageSource : MessageSource() {
         final override val targetId: Long get() = target.id
 
         abstract class ToFriend : Outgoing() {
+            companion object Key : Message.Key<ToFriend>
+
             abstract override val target: QQ
             final override val subject: QQ get() = target
             //  final override fun toString(): String = "OnlineMessageSource.ToFriend(target=${target.id})"
         }
 
         abstract class ToGroup : Outgoing() {
+            companion object Key : Message.Key<ToGroup>
+
             abstract override val target: Group
             final override val subject: Group get() = target
             //  final override fun toString(): String = "OnlineMessageSource.ToGroup(group=${target.id})"
@@ -148,6 +150,8 @@ sealed class OnlineMessageSource : MessageSource() {
      * 接收到的一条消息的 [MessageSource]
      */
     sealed class Incoming : OnlineMessageSource() {
+        companion object Key : Message.Key<Incoming>
+
         abstract override val sender: QQ // out QQ
         abstract override val target: Bot
 
@@ -155,12 +159,16 @@ sealed class OnlineMessageSource : MessageSource() {
         final override val targetId: Long get() = target.id
 
         abstract class FromFriend : Incoming() {
+            companion object Key : Message.Key<FromFriend>
+
             abstract override val sender: QQ
             final override val subject: QQ get() = sender
             // final override fun toString(): String = "OnlineMessageSource.FromFriend(from=${sender.id})"
         }
 
         abstract class FromGroup : Incoming() {
+            companion object Key : Message.Key<FromGroup>
+
             abstract override val sender: Member
             final override val subject: Group get() = sender.group
             val group: Group get() = sender.group
@@ -207,6 +215,7 @@ inline fun MessageSource.recallIn(
  */
 @SinceMirai("0.33.0")
 abstract class OfflineMessageSource : MessageSource() {
+    companion object Key : Message.Key<OfflineMessageSource>
     // final override fun toString(): String = "OfflineMessageSource(sender=$senderId, target=$targetId)"
 } // TODO: 2020/4/4 可能要分群和好友
 
diff --git a/mirai-core/src/jvmMain/kotlin/net/mamoe/mirai/BotJavaFriendlyAPI.kt b/mirai-core/src/jvmMain/kotlin/net/mamoe/mirai/BotJavaFriendlyAPI.kt
index 3974289d2..2958730af 100644
--- a/mirai-core/src/jvmMain/kotlin/net/mamoe/mirai/BotJavaFriendlyAPI.kt
+++ b/mirai-core/src/jvmMain/kotlin/net/mamoe/mirai/BotJavaFriendlyAPI.kt
@@ -5,7 +5,6 @@ import net.mamoe.mirai.contact.PermissionDeniedException
 import net.mamoe.mirai.contact.recall
 import net.mamoe.mirai.data.AddFriendResult
 import net.mamoe.mirai.message.MessageReceipt
-import net.mamoe.mirai.message.data.ExperimentalMessageSource
 import net.mamoe.mirai.message.data.Image
 import net.mamoe.mirai.message.data.MessageChain
 import net.mamoe.mirai.message.data.MessageSource
@@ -62,7 +61,6 @@ actual abstract class BotJavaFriendlyAPI actual constructor() {
      *
      * @see Bot.recall (扩展函数) 接受参数 [MessageChain]
      */
-    @ExperimentalMessageSource
     @JvmName("recall")
     fun __recallBlockingForJava__(source: MessageSource) {
         runBlocking { recall(source) }
@@ -90,7 +88,6 @@ actual abstract class BotJavaFriendlyAPI actual constructor() {
      * @param millis 延迟的时间, 单位为毫秒
      * @see recall
      */
-    @ExperimentalMessageSource
     @JvmName("recallIn")
     fun __recallIn_MemberForJava__(source: MessageSource, millis: Long) {
         runBlocking { recallIn(source, millis) }
@@ -151,7 +148,6 @@ actual abstract class BotJavaFriendlyAPI actual constructor() {
     /**
      * 异步调用 [__recallBlockingForJava__]
      */
-    @ExperimentalMessageSource
     @JvmName("recallAsync")
     fun __recallAsyncForJava__(source: MessageSource): Future<Unit> {
         return future { recall(source) }
diff --git a/mirai-core/src/jvmMain/kotlin/net/mamoe/mirai/message/MessageReceipt.kt b/mirai-core/src/jvmMain/kotlin/net/mamoe/mirai/message/MessageReceipt.kt
index 7b52cfd9f..837794f86 100644
--- a/mirai-core/src/jvmMain/kotlin/net/mamoe/mirai/message/MessageReceipt.kt
+++ b/mirai-core/src/jvmMain/kotlin/net/mamoe/mirai/message/MessageReceipt.kt
@@ -11,7 +11,6 @@ import net.mamoe.mirai.contact.Contact
 import net.mamoe.mirai.contact.Group
 import net.mamoe.mirai.contact.Member
 import net.mamoe.mirai.contact.QQ
-import net.mamoe.mirai.message.data.ExperimentalMessageSource
 import net.mamoe.mirai.message.data.Message
 import net.mamoe.mirai.message.data.OnlineMessageSource
 import net.mamoe.mirai.message.data.QuoteReply
@@ -24,16 +23,18 @@ import net.mamoe.mirai.utils.unsafeWeakRef
  *
  * 此对象持有 [Contact] 的弱引用, [Bot] 离线后将会释放引用, 届时 [target] 将无法访问.
  *
+ * @param source 指代发送出去的消息
+ * @param target 消息发送对象
+ *
  * @see Group.sendMessage 发送群消息, 返回回执（此对象）
  * @see QQ.sendMessage 发送群消息, 返回回执（此对象）
  *
  * @see MessageReceipt.sourceId 源 id
- * @see MessageReceipt.sourceSequenceId 源序列号
  * @see MessageReceipt.sourceTime 源时间
  */
 @Suppress("FunctionName")
 @OptIn(MiraiInternalAPI::class)
-actual open class MessageReceipt<out C : Contact> @OptIn(ExperimentalMessageSource::class)
+actual open class MessageReceipt<out C : Contact>
 actual constructor(
     actual val source: OnlineMessageSource.Outgoing,
     target: C,