Hi Tim,
Thank you for the helpful information. Here is how hotmail and yahoo both decide to read HTML. Yahoo will only read standard HTML correctly, and does not support anchor links on all browsers, and will clip long newsletters. Hotmail will read only standard HTML, and you must use inline styling and will disable background images (you must turn authentication on in your account for this not to be an issue), it does have some CSS issues, and text may appear to be underlined. Click here to read our post on Constant Contact Authentication.
Also, to see how most email clients read HTML and any known issues with them click here.
Ken
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