You build a beautiful just-listed graphic, drop the whole thing in as one image, and send it. To a spam filter that email contains no words at all, which is one of several reasons your prettiest emails are the ones nobody reads.
This is a live training session on email templates, and the first half is entirely about getting delivered before anyone worries about design. The rules, in the order she gives them:
Do not send a heavily designed template to a brand new contact. If someone has never had an email from you and the first one arrives full of "HTML and pictures and buttons and links", the carrier reads it as a promotion and files it accordingly. Warm up with your engaged contacts first.
Keep the words in proportion to the pictures: "maintain a balance of 6040 text to um picture or media ratio." Her reason is that filters need something to read. If they only have a line or two of text "to gauge it on, it's probably going to go to spam".
Which kills the most common shortcut, pasting a finished design in as one image. "There might be a bunch of text in that picture, but that's not text to an email carrier." A colleague on the call names what happened to it: flattening "takes all of the individual boxes that you have and it squishes it all in, flattens it into one image", and "it's going to backfire on you".
Size the images: "file size of your pictures to be under 200 kilobytes", and on dimensions, "You don't want a a max width of 600 max when you're putting these in there." Oversized images load slowly and long emails get clipped by the inbox.
Write real alt text, both for readers using a screen reader and for the case where images are blocked. Not a picture of a blue house, but "a fourbedroom, three bath house in Westland and the open house is Sunday", so a recipient can tell from the blocked image whether they want to load it.
Never hide the link inside the picture: "email carriers don't like this because they feel like you're trying to hide the links inside of pictures and that is a surefire red flag for them to send something to spam." Use a button, and label it with the thing itself. "Don't put click here. Tell them what they're clicking on and why."
Skip the link shorteners, even the one built into your own platform, and use the full verified link so the carrier can see where it goes. And include "a clear one-click unsubscribe".
“maintain a balance of 6040 text to um picture or media ratio.”
Almost every one of these rules is the same rule: a spam filter can only judge what it can read, and every design shortcut takes away something readable. One image instead of text, a shortened link instead of a domain, a picture instead of a button, click here instead of a label. Each of them makes the email prettier to you and blanker to the machine deciding whether anyone sees it.
That is why the flattened graphic is the expensive one. It is the shortcut that feels most like professional work, it takes the longest to make, and it converts your entire message into zero words. If you only change one thing, rebuild your just-listed email as real text with two or three sized images and a labeled button, then send it to yourself at a couple of different providers and see which folder it lands in. That test costs five minutes and tells you more than any subject-line advice.