Question about Data Processing Basis

Question about Data Processing Basis

Hello,

I have several lists that are considered B2B email marketing.  The emails that are sent are to our external sales teams/distributors/sales partners.  These companies help us sell our products to our customers.  Therefore, the emails we are sending are product related and sent to those contacts that were provided to us by their company.

Would these be considered legitament interest, consent required or contract?  The LI choice asks for an attachment.  

Any help would be appreciated!

Thanks