Campaign images arrive as a folder: hero, three product shots, two logos, a testimonial headshot, a footer mark, and whatever the designer exported for the app-block. Compressing them one at a time means seven quality-slider decisions and a real chance that the campaign ends up with a 90 KB hero next to a 1.4 MB product shot — which is the wrong way round, because the hero is what the reader sees first. A batch pass replaces that with one decision: set a byte target and a width, drop the folder in, and every image comes back at a weight you chose. Two things still need your judgement and can't be automated away. Format: Mailchimp lists JPG, GIF and PNG as the formats that display reliably across email clients, and a logo or a flat-colour mark compresses far better as PNG than JPEG while a photograph does the reverse. Transparency: flattening a transparent PNG into JPEG produces a white or black box behind your logo, which is a visible bug in every client. Skwish keeps formats separate and lists before-and-after per file, then hands the whole prepared set back as one ZIP.