c++, Is there any good solution for Message Sender to support send method about various type?

I want to make MessageSender to support send method about various type and satisfy followings conditions.

condition A) 'send XXX Type Message' can be added later (=Easy to expand)

condition B) each sendXTypeMessage is called in other thread (=Each method needed to be thread independent)

first my thinking was followings

class MessageSender
    {
    public:
     sendATypeMessage(ATypeData)
     sendBTypeMessage(BTypeData)
     sendCTypeMessage(CTypeData)
     ...(it can be added other type later)
    }

But in case of this, when I want to add sendDTypeMessage(data). I have to modify MessageSender class.

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second my thinking was followings

class XTypeData : public IMessage
{
...
}
class MessageSender
{
public:
 sendMessage(const IMessage& data); 
}
MessageSender::sendMessage(const IMessage& data)
{
1) mutex lock
2) switch(check message type)
3) do something...
}

but in case of this, I have to use mutex lock in sendMessage.

then it can cause performance issue because each message sender thread can be blocked in sendMessage.

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Is there any good solution to satisfy these conditions?