send-hook my_hdr unknown variable

[Joseph <syscon@xxxxxxxxxxxxx>]

Is there a limit how many variable I can assign to a hook?
I have below:

send-hook . 'unmy_hdr From:'
send-hook '~t ^xxxx@xxxxxxxxx' 'set signature=~/.mutt/signature-personal' 
'my_hdr From: Joseph <xxxxx@xxxxxxxxxxxx>

The signature part is working but my_hdr gives me "unknown variable" 
when I try to compose a message.

-- 
#Joseph
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