Mail app only sending through my google email account.

Hello, I saw this was an issue for someone else a few years ago. I read that thread and had tried most of what was discussed. All was working fine I have three email addresses. My primary one with Virginmedia, and a third party one that is also associated with my Virginmedia account. I also have a gmail address.

I usually use my primary address for day to day emails and the third party email address associated with my website. Rarely did I use the google account. I recently find that I can only send mails via the google address.

Virginmedia advise that all is as it should be within my settings although a message I get from mail is as below:-

Any advise would be appreciated.

thanks.