It could be that your email sending/server does not have the correct authentication and is being seen as potential spam. Most cases this is because there are missing or incorrect DNS settings in your domain details.
I would recommend checking your email sender with MxToolBox. Follow the on screen promts and it will let you know if there are any issues with your domain DNS.
Within the profile when logged in the user can select and add their own cover image. This will allow all users to have their own unique cover images.
You might want to make sure your images are not too big and the correct proportions otherwise they will be cropped. Depending on your theme this size might vary but a good starting point would be 1350px wide and 350px tall or for full screen width 1920px x 640px.
