Reply filled the address and it is throwing an error to the user

Reply filled the address and it is throwing an error to the user

When I clicked 'Reply' it automatically filled the TO with an address alongwith comma but when I click send it is throwing error. If comma is forbidden can you automatically desist from filling it in the first instance.

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Deepak Vasudevan
http://thamizhththendral.blogspot.com/