I have run into this problem before.  I think it occurred when we made a change to the System Administrators email address.  What I found is that when a change is made to the SA email address, the email address that was stored in the workflow email is lost.  

Sorry this posted before I was done.  Go to work workflow email and see if there is a "from".  You might find that it is empty.

If that is the case then please can you log a bug with the support team?

Yes. This worked like a charm. 

Thanks

This might be true. I have made changes to SA email address and then changed back to original.  But never thought it will effect the workflow also.

Could you log this as a case with your local support team?  This type of behaviour should be caught.  Thanks

Okay, Noted. Thanks

Sure. Will do. Thanks.

Glad to hear this worked out for you. 

I am curious as to which version of CRM you are using.  I have had this happen to me on several different installs...but I don't recall the CRM version.

The first time it happened, I had severe "egg on my face"  because I was on a conference with the client and their IT team trying to figure the error message out.  Imagine my surprise when there was NO from address in the email that was trying to be sent!!  I was so surprised as I had recently checked it.  I filled it in.  Confirmed that it saved.  Went to the admin user, changed the email address and then went back to the workflow again.  Email was gone!  That saved a little "egg".

I have not forgotten that experience! :-)

Hi Michele,

The version is CRM 2018 R3. Your experience, helped me to  get a solution.

Many Thanks