Find duplicated items in AD

Hi

I'm in the process of migrating to Exchange 365.  I've got the Sync tool running OK and all my accounts/users in 365 but it reports a duplicate entry error.

We did have a distribution list 'accounts@xxx.xxx' which I did delete some time ago so I could setup as an email enabled security group.

I'm guessing AD has a record of the old dist list and 365 doesn't like it.

Where do I find it?

Thanks

Daren