Mail Merge - unable to send more than 50 email

Mail Merge - unable to send more than 50 email

Hi,

I've subscribed to the pay email service because of the Mail Merge feature. However, I've found that this feature only allow to send up to 50 emails. I've to attach a screenshot for your reference. 
This limitation is not mentioned anywhere in service. Is there way to increase the limit? 50 is pretty much useless to us.

Thanks,
Frankie