NUPGRADE falling over on emails with 5-+ Recipients

I’ve been converting a number of PST files from Exchange into Mail files using the NUPGRADE 3 tool. This for the most part works ok.
However, I’ve noticed that it completly falls over when it tries to migrate an email which has 50+ people in the “TO:” of the email.

This is time consuming to keep re-migrating when you have removed the offending document from the PST.

So the questions are :

a) Is there an automatic workaround/fix ?

b) Is there a way in Outlook to view all your mails which have > 50 people in the Recipients field ? So that I can then delete these manuall before migration.

c) Any other way to filter out these 50+ type emails. ??

Many thanks in advance.

Cheers
Andy