https:// in url images

Hello, the temrinar to arm my newsletter does not show me the pictures.

In the preview, the src attribute of the img tag goes like this:
<img src="//mysite.com/wp-content/..." />

This means that in an email, where I am not located on my site, the picture is not. The URL of the image should bring the http: //

This is a plugin configuration? suggesting to correct this ??
I am willing to modify some code if so required.

Thank you very much.

https://www.ads-software.com/plugins/wysija-newsletters/