Outgoing Email Blocked by Norton IS - Email Error 571

Hello -

 

I am running Norton IS v.19.9.0.9, with MS Vista Home Pro & MS Office 2007.

 

When sending email via Outlook, sometimes I receive a message:

"Email Error

571 sorry, reached maximum number of recipients for one session (#5.7.1 - chkuser)"

 

I've checked with my ISP, and they say that message/error is generated by NIS, and NIS is responsible for blocking the send.  This error occurs when I have a large number of recipients in the To, CC, or BCC lines.  The email does show up in my Outlook Sent box, but no recipients acknowledge receiving the email.

 

Where can I find the setting to change the limit of recipients in one email?  That appears to be the problem - not the number of emails sent per day or time period.  I can send an email to a single or few individuals immediately after receiving the error message.

 

Thanks for any help or advice you can provide!

 

Paul