thanks for your help.
now i point MX record to my public IP.
now i have others problems but there are not from zimbra. My ISP cannot do relay and i cant set a forward rule to port 25 to my zimbra server so iŽll try to download emails with fetchmail but for this, i need one external account for each internal account and it will be impossible because my ISP only allow me 10 accounts.
zimbra:/home# dig mydomain.es mx
; <<>> DiG 9.5.1-P3 <<>> mydomain.es mx
;; global options: printcmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 50569
;; flags: qr rd ra; QUERY: 1, ANSWER: 2, AUTHORITY: 0, ADDITIONAL: 1
;; QUESTION SECTION:
;mydomain.es. IN MX
;; ANSWER SECTION:
mydomain.es. 300 IN MX 20 mail.mydomain.es.
mydomain.es. 300 IN MX 10 my public IP.
;; ADDITIONAL SECTION:
mail.mydomain.es. 300 IN A my public IP
;; Query time: 81 msec
;; SERVER: 192.168.0.200#53(192.168.0.200)
;; WHEN: Wed Oct 7 14:53:59 2009
;; MSG SIZE rcvd: 102