I was able to get it to work following these settings up to step 9. Inbox.com - Email Help
If you notice #10, that step is for those who cannot use port 25 with their ISP.
If that STILL doesn't work, you may want to give your ISP's outgoing SMTP server a shot. If you do, make sure you click MORE SETTINGS, OUTGOING SERVER, and choose "logon using" like the image below: