Everytime I try to send a message to more than 4 recipients I get a "451 4.5.3 No more transactions allowed" message from NIS. I have to turn off "Scan outgoing email messages"...
I use NIS 2011.
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What program are you using for email? What are the email ports that are required by your ISP. The message you are receiving is most likely from your ISP. Norton acts as a go between for your ISP's email server. If they send a message, then Norton displays it. Thanks.
Norton will display error messages from your ISP, making it appear that Norton is causing the issue when it is only relaying information from your email service provider. So it may be that you are running up against an anti-spam measure that your ISP imposes that limits the number of messages that can be sent at one time. Who is your email service provider?