hello,
are you saying that you cannot send recevie any emails on exchange server after configuring what you did.
another question, after looking at your global and nat command it loooks like you are only making one IP to be natted which is trying to reach outside and it is your exchange server ip address.
therefore if that is that case then most likely you don't need global and nat all you need to do is configure static and have ACL to allow SMTP and POP3 on the outside interface like below
//to allow smtp
access-list acl_out permit tcp any host 202.X.X.43 eq smtp
//to allow pop3
access-list acl_out permit tcp any host 202.X.X.43 eq pop3
//to allow web access
access-list acl_out permit tcp any host 202.X.X.43 eq https
//to apply ACL on the outside interface
access-group acl_out in interface outside
HTH, please rate if it does