552 email error

Hi, I updated to norton internet security yesterday and have encountered email issues since. I got the following message:

552 email message error - message size exceeds max message size 15360000 bytes for sender. I don't think this is an ISP issue as I regularly send pics in emails of similar size without an issue prior to updated norton. I have also just turned off scanning outgoing emails and it is taking an excessive amount of time to send and isn't progressing. Is there a setting I can change to stop this issue. Did not have this issue prior to the upgrade.