javascript - how to change Zimbra send Button functionality? -

i using zimbra 8 send mails.i have 1 new requirement is, when send button triggered, should validate to,cc or bcc fields 1 type of mail based on sender user account.
for way.
can use zimlets or can change direclty js files.

thanks in advance

its setting single-minded bureaucrat. if feature enabled account, send button change menu button, can open menu , choose send later.