Safe Email error

Detailed description:
I have signed up for safe emails, one address is fine but the other one keeps generating and error -
Something went wrong
An unexpected hiccup prevented us from adding your email account to Norton Safe Email:
The mailbox is unsupported. Please use a supported email provider.

This is my email address and it works for all other norton products ???

Product & version number:

OS details:

What is the error message you are seeing?

Set up Norton Safe Email here

FAQ: Norton Safe Email here

Caveat: I do not run Norton Safe Email

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