need help to sync mailbox with existing domain and dns records

i need help and still new on virtualmin im running on UBUNTU x64 server and i have been installed successfully, now i have other problem and i want to ask

1. i have existing domain hosting and i want to sync with my domain xxx.com , i have been set my hostname , mail username , and password same as my existing domain but why my inbox is not synced ? but i can send mail.

note :
- telnet to my ip address 172.22.1.78 port 110 and 587 is ok.
-

2. im leave dns records as default like this :

$ttl Default Cache Time 38400
xxxx.com SOA - Start Of Domain xxxx.com. root.xxxx.com. 1377950781 10800 3600 604800 38400
xxxx.com NS - Name Server xxxx.com.
xxxx.com A - IPv4 Address 172.22.1.78
www A - IPv4 Address 172.22.1.78
ftp A - IPv4 Address 172.22.1.78
m A - IPv4 Address 172.22.1.78
localhost A - IPv4 Address 127.0.0.1
webmail A - IPv4 Address 172.22.1.78
admin A - IPv4 Address 172.22.1.78
mail A - IPv4 Address 172.22.1.78
xxxx.com MX - Mail Server 5 mail.xxxxcom.
xxxx.com SPF - Sender Permitted From v=spf1 a mx a:xxxx.com ip4:172.22.1.78 ?all

does something wrong ?please guide me , and thanks verry much for your help