Network Prevent for Email - size issues

We have had a few instances now that the queue sending to DLP email prevent server gets backed up.  I haven't fully figured out what size attachment it chokes on, so far it seems to be an attachment over 200MB (I know, we allow large attachments).  The main problem is, when this happens any emails after that going to the same domain also get stuck in the queue until the large message is removed.  So few questions:

1.  Is there a limitation to attachment size that DLP can really handle realistically?

2.  Is there anything I'm missing as far as why it would hold up all emails to that same domain?  Exchange generally doesnt work that way.