Mail works fine - except for one address.

ed boy Said:

"Thanks for your response I will try your first suggestion. My iCloud email address also does not get a message through so I am reticent to remove my account from mail."

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You are welcome.

Three Thoughts...

Did Gmail Work?:

• Was logging in to Gmail and sending it successful?

Use Another Mac:

• As for your second sentence: If you have another Mac to use, try adding this account, and see if you still get this error.

If the above are unavailable not an option, then....

Create a New Admin User:

• If this ends up not being fixed, then I would go about creating a new Administrator account. While logged in to it, try setting this all up and send it with the user's Mail app. If it works, then there is obviously something misconfigured with this current user. So, transfer everything over to this new Administrator user, then trash the current user. You should be all set from there, with a new user.

ed boy Said:

“Mail works fine - except for one address:

I am unable to send my partner an email. Mail seems to send it and it goes into the Sent folder but it never arrives. If I add another[...]”

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Log in to Gmail:

What happens when you send it through use of Gmail? Does the same issue occur?

If yes, then that is something in their end.

If not, then remove this eMail Account from Mail. Then add it back.

For Note:

Contact your eMail Provider: Google

I would also contact Google to see what feedback they have for you.