SMTP -ORA-29279: SMTP permanent error: 501 5.5.4 Invalid domain

 Dear friends,

We are using our own script to trigger database availability and etc.. autogenerated mail alert.

We used SMTP address which is configured in Domino, which it was working fine.

Now company decided to change SMTP configued in Exchnage server. If i change the ip address it is giving error "ORA-29279: SMTP permanent error: 501 5.5.4 Invalid domain"

Kindly help me , Thanks in Advance

1.PMAIL Code:

2. The another script capture the data and send it daily

1.

Create or  REPLACE PROCEDURE PMAIL(
p_sender in varchar2 ,
p_subject in varchar2 ,
p_body in varchar2
)

is
v_mailhost constant varchar2 (18):='prajas@yahoo.com'