Q: Outlook365 Email Is Not Sending in Mail

Hello SEP1234,

I understand that you are unable to send email from the Mail app on your Mac. Let's see if we can get that sorted out. 

The first thing I would look at is using Connection Doctor for your Mac. This will help determine why your email from GoDaddy is not able to send messages. You could see issues with ports and all you would need to do is double click the section that is giving you trouble and it will take you to the place that is need to make changes. These steps may also address the repeated prompts to enter your password. Take a look at the articles below for steps on using Connection Doctor as well as troubleshooting the Mail app relating to sending and receiving emails. 

Use Mail Connection Doctor
https://support.apple.com/en-us/HT204173​

If you can’t send or receive email on your Mac
https://support.apple.com/en-us/HT204075

Because you mentioned that you are using GoDaddy and specifically Outlook 365 version, I have found some troubleshooting on GoDaddy's website that should help you out if you are still unable to send email. While looking over these articles, I noticed that it looks like it is recommended to use the Exchange setup when configuring your account over POP. Look over these articles as well to get you sending out those important emails for work. 

APPLE MAIL: SETTING UP WORKSPACE EMAIL
https://www.godaddy.com/help/apple-mail-setting-up-workspace-email-4874​

APPLE MAIL (MAC): SET UP EMAIL
https://www.godaddy.com/help/apple-mail-mac-set-up-email-8903​

SETTING UP YOUR EMAIL ADDRESS WITH POP
https://www.godaddy.com/help/setting-up-your-email-address-with-pop-4715​

WORKSPACE EMAIL HELP
https://www.godaddy.com/help/troubleshooting-apple-mail-setup-9319​

Take care