We've added a ton of functionality to the Seatrobot Contacts management area over the last few months. It's now easier than ever to upload any number of contacts from .xls and .csv files - and sort and group them into lists, so you can use them as contact lists to send invites to.
In Contacts (in the purple bar), click on the multiple users upload button (above). Now, you'll see step by step instructions for creating a new Contact List, or adding new contacts to an existing Contact List. Follow through the steps to upload your contact files.
Seatrobot will also de-dupe your list as you upload it (by cross-checking email addresses) and will give you a report after your upload on how many unique contacts were actually added to your contact database.
Note that Seatrobot will only upload contacts which have email addresses. Be sure to mark one of your column headers as 'email' when matching the columns in your .xls file to Seatrobot's inputs.