100+ Undelivered mail received in just small amount of time

[Mady]

Hi,

Can you help me identify why our one email user received 100+ undelivered mail notification in just 30 mins. Do I need to modify any settings on our ESA? Please advise. 

Below is snippet of the undelivered mail.

Delivery has failed to these recipients or groups:

abcd@aol.com
A problem occurred during the delivery of this message to this e-mail address. Try sending this message again. If the problem continues, please contact your helpdesk.

The following organization rejected your message: [x.x.x.x].

Diagnostic information for administrators:

Generating server: mail.domain.com

abcd@aol.com
[x.x.x.x] #<[x.x.x.x] #5.0.0 smtp; 5.1.0 - Unknown address error 550-'5.1.1 <abcd@aol.com>: Recipient address rejected: aol.com' (delivery attempts: 3)> #SMTP#

Thank you and regards,

Mady

[Libin Varghese]

Hi Mady,

You can review the mail_logs for the bounce emails received on the ESA to see what the sending server IP was.

If these are illegitimate bounces I would recommend enabling bounce verification feature on the ESA as described in the below article.

http://www.cisco.com/c/en/us/support/docs/security/email-security-appliance/117918-technote-esa-00.html

- Libin V