When this happens in case it is an exchange email server to exchange
email server communication it means:
that the FQDN is not correctly set in you exchange server (recipient).
for that you go in the exchange server (mmc) management console look
for:
- Protocoles
- default virtual SMTP server
Right mouse click on Properties of SMTP virtual server
Then on the "Delivery" (Remise in French) tab (last one to the right)
Then click on "Advanced Options/ Settings"
you should see there the field where the FQDN is set for your exchange
server.....
it has to match you DNS MX Record !
if your DNS MX Record says
You can use "NSLOOKUP" with set type=all to check your DNS MX record.
as in from DOS COMMAND PROMPT:
NSLOOKUP
set type=all
mydomain.com
blabla blabla and where you see:
mydomain.com MX preference = 10, mail exchanger = toto.mydomain.com
Then you field Fully Qualified Name should READ: toto.mydomain.com