This is unlikely to be a portainer issue and more a config issue with that server in npm. Bit hard for us to troubleshoot without seeing the real error behind this. What does a browser like edge tell you? What does this one say say if you click details?

Agreed, I moved all mine from godaddy to cloudflare to save money. My email is with M365.

simple version:

1. save your existing mail locally

2. point the DNS record of your domain name at whatever new service you are buying (they should have instructions on that)

3. import some / all / none of the mail you saved locally to the new service as you see fit

now your email will come and go from your new mail service