Difference between forward and tell in akka actors

The sender() will be different on the receiving end.

Message sends using tell (also known as !):

A tells message M to B.
B tells that message to C.
C thinks the sender() of message M is B.

Message sends using forward:

A tells message M to B.
B forwards that message to C.
C thinks the sender() of message M is A.

Worth pointing out is, that you can achieve the same as forward when explicitly setting the sender of a message using tell, however this is not typical Akka-style:

// inside `B`, when received `msg` from `A`
C tell (msg, A) 
      == 
C forward msg

For more info refer to the docs about forward.