Hmm, looking at it we return a list of blocked senders and signatures as well as a couple settings. I could maybe see a very large signature causing an issue? Could you check this user's blocked sender count, it would have to be astronomical to be 11mb though. Another thing to check is their signatures, and more specifically if they've some how managed to embed an inline image or something like that INTO their signature. I could see that causing an issue as well.
If you don't see anything odd, you can try checking that user on your system and seeing if they have any large JSON files in their directory, C:\SmarterMail\Domains\<domain>\Users\<user>
Let me know if you see anything.