Should 'Server Default' with Mailer work with Digital Ocean?

I am following the Password Reset Functionality doc and get the following error when submitting the password reset request:

{"status":"500","code":"ENOENT","message":"spawn sendmail ENOENT","stack":"Error: spawn sendmail ENOENT\n    at Process.ChildProcess._handle.onexit (internal/child_process.js:267:19)\n    at onErrorNT (internal/child_process.js:469:16)\n    at processTicksAndRejections (internal/process/task_queues.js:84:21)"}

I haven’t send emails before, so I’m guessing the issue lies in the Setup Mailer.

What is going wrong here? The set up or should I not use ‘Server Default’ when using a Digital Ocean droplet?

My set up:

(using NodeJS and remote digital ocean droplet)