Background Images
Basically, background images are not an option at all if you need the support of a wide range of email readers. This mainly applies to Outlook 2007 and later, as well as Hotmail (not yet tested Outlook.com).
If the PSD has a large area with a bg image but no text on it, you can cut off this part of the email as a foreground image.
If there is textual content in the same area, there are 3 options:
- Skip general image bg.
- Implement a bg image with embedded CSS and strive for elegant degradation (assuming that the letter will not look so good in some email readers).
- Edit this part of the letter as one foreground image (with text on the image). The risk of cutting text in an image is that it affects usability (many email readers block external images by default), it compromises accessibility, and most importantly, if the ratio of text to images becomes too low, it will cause spam filters . Therefore, it’s nice to make as little as possible (cutting text in the form of images). But from time to time it is usually safe.
Before you select option 1 or 2, you probably need to clear it by the development team. And before making a large selection of option 3, it would be wise to test it in various spam filters.
The influence of bg images in HTML emails and the need to minimize them should be reported to developers early and often, as problems with it are not well-known among them, even among the best of them.
Rounded corners
As @samanthasquared mentioned, rounded corners are poorly supported in email readers. They should be implemented as images (or, as in the case of background images, skip them one by one or choose elegant degradation, if this is acceptable for the development team).
You can reduce the total number of images that the user must download if you cut one image for the entire top and one image for the entire bottom, rather than cutting separate images for each individual corner. Fewer images mean faster downloads and less risk of triggering spam filters.