Aim for an overall email size of 100KB. The closer your email is to this recommended size, the more likely it’ll be accepted by receiving servers. Aim for a balanced image-to-text ratio; this is best practice. Most servers can’t ‘read’ images or identify what they contain, so receiving servers may interpret emails consisting only (or mostly) of images as spam. A balanced HTML email is more likely to be delivered.
Any email in our system that’s over 350KB will only send to contacts for 20 minutes every hour.