The process of sharing a markup with your colleagues is the same as sharing a markup with your accounts.
Click Shares at the bottom of your screen, and then select the people with whom you’d like to share your markup.
-There is a cap on the number of emails that can go out at once. That cap is 298. If you need to send more than that, you’ll just want to break your list up into smaller chunks.
You can also take your markup and export it to an excel document, which you can then send to your colleagues via email, or even upload to a document sharing tool like Google Drive, SharePoint, etc. You can then work on that spreadsheet with your colleagues and share the workload of creating good markups.
More about importing and exporting markups here.