I cannot install my inbox into Outlook

My inbox works well on the comcast.net web portal but when I add it in Microsoft Outlook (the legacy version) following the instructions, it does not allow to install. The password dialog box keeps coming and when I input the right password, it won't work. This happens for one of my two inboxes.  I would also like to mention that I installed that inbox in Outlook new but I can only receive email but I cannot send. I get this error message: Smtp submission failed. Server 'smtp.comcast.net' Port '587'. --> Unexpected SMTP server response. Expected: 235, actual: 535, whole response: 535 5.7.0 ...authentication rejected Failure code: 14fd.

Could you please assist?