OOF is not working for External client

HI,

We have Exchange 2010 with Sp1. Since last few days OOF is not working for External client. It was working earlier.

I have tested

1.

When I browse to EMC > Org. Configuration > Hub Transport > Remote Domains > Default (Properties)

"Allow external out-of-office messages and legacy out-of-office messages (configured by using Outlook 2003 or earlier clients, or configured on Exchange 2003 mailboxes)" is checked.

Under "Message Format", "Allow automatic replies" and "Allow automatic forward" are both checked.

2. I have disabled Anti virus on server

Kindly Advise.