The `loading="lazy"` attribute was set by default on all images but this affected the `mass_mailing` module as well while that attribute doesn't work in emails and can cause some issues in edition. One known such issue this addresses is to be reproduced as follows: 1. Create a new mail 2. Drop the "cover" snippet It has height 0 so it won't load until another snippet (with a non-zero height) is dropped. task-2761074 closes odoo/odoo#84415 Signed-off-by: David Monjoie (dmo) <dmo@odoo.com>