SendMessage is a blocking call.  ie., when a SendMessage() 
API is called from an application, the lines written after 
this API call cannot be executed until the message is 
processed and returned by the window procedure.

Whereas PostMessage() just posts the message into the 
windows corresponding message queue and returns immediately 
irrespective of the message is processed or not.

SendMessage is calling window proc and waiting for reply. 
where are PostMessage api is sending message in message 
queue and will not wait. Then message will be in Message 
queue till it will not be proceded by window proc.

In sort SendMessage waits till processing completion where 
as PostMessage does not wait.

Both are Win32 API members.

SendMessage(...) its NonQueued Messages. 


PostMessage(...) its Queued Messages.

SendMessage(...) Meassages can also be placed in a message 
queue by calling PostMessage(...).

send message doesn't follows message loop route.
while post massage follows.

examples of send message:WM_QUIT
examples of post message :WM_CLOSE,WM_COMMAND,...