Please provide more details to enable faster resolution.
The version of Integration Server you are working with? Some features may have been enhanced in later versions, best to specify the exact version / core fix details.
Define “large data”, what is the largest data that is successfully sent out, at what point does it break?
Are there any messages in the Integration Server logs?
What is the result when pub.client:smtp is executed?
Is it required to send it as an email attachement?
If not then use SFTP or another way that is better suit for sharing large files.
If yes then the options are probably to compress the file (won’t do much for large files IMO), split them into chunks (but when received they need to be combined back) or ask the email service provider to increase the attachement max file limit (again there will be a limit).
As reamon mentioned the size of the attachment you are trying to send is exceeding the maximum size limit of the email server. Did you try sending it from the email client?
Also, you could consider storing the JSON data in a file or a database, and sending a link to the file or database record in the email instead of the entire data itself. This approach can also help in cases where the recipient might have trouble receiving large attachments.