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Hi Nick, thanks for help.
yes, [email protected] is users, so I have delete and recreate the user and change the password stronger, reinstall os client and disable android access.
I have 3 office witch 2 of them in the external network (access by internet) an so many user access by smartphone, so I can not use trusted network concept
for encryption type I set none.
my friend said that I have add reject_sender_login_mismatch rule, so the spam can not send email with different account
for this case I have test my smtp with this configuration
I can send email use unknown email but with real account and password.
I have try googling for add reject_sender_login_mismatch rule postfix, but I am not sure about the right script.
Thanks. -