GWIA: Status Msg Error: 25087 521C9A8d:F38:0:62337

Hi,

Received this error in GWIA log:

12:24:49 AF8F MSG 3488493 Sender: <sender's e-mail>
12:24:49 AF8F MSG 3488493 Building message: s21c9a91.518
12:24:49 AF8F MSG 3488493 Recipient: <Recipient's e-mail address>
12:24:50 B097 MSG 3488493 Status Msg Error: 25087 521C9A8D.F38:0:62337

In the sender properties page, the delivery status showing as "Pending".

Found no error code associated with 25087, anyone has any ideas of what is going on?

Thanks in advance.