Fail create email ticket

[bighorn]

i'm using otrs 2.4.8.

Previously tested, as agent i can create email ticket and the ticket was emailed to recipient.(normal)
But now, i can't create the email ticket because it gave error for the email address:

* invalid xxx@biruni.upm.my (no mail exchanger (mx) found!)! invalid yyy@utm.my (no mail exchanger (mx) found!)! invalid zzz@gmail.com (no mail exchanger (mx) found!)!

* invalid 12345@yahoo.com (no mail exchanger (mx) found!)!

I've checked the sendmail service is running.....
Those email address is valid email address
OTRS system email is in valid state
postmaster mail acc and auto response working...

please help...

[jojo]

there is no MX Record in the DNS. You can switch of the check via sysconfig