Each Sortd account is directly mapped to your Google account, so you cannot have one Sortd account linked to multiple Gmail addresses. However Sortd's team and email sharing functionality allows emails linked to tasks/items on a shared Sortd board to be shared with all Sortd users (accounts) on that shared Sortd board. This functionality only shares email on a shared board and does not share or otherwise allow other Sortd accounts to see the email in a users Inbox/folders or non shared boards. Note that this will only work for boards you create under an organization on a team plan, since your personal (private) board cannot be shared.
Another possibility is to use Gmail itself to link multiple accounts. To do this you can add multiple accounts in your Gmail settings under the Accounts tab and manage all your mail and Sortd boards from a single Gmail login.