Lotus Notes email client is one of the more frustrating ones out there (next to Outlook PC). It's a very low percentage of email clients and primarily used by larger companies, if any.
Common rendering issues in Lotus notes
Red Boxes around Images in Lotus Notes Email
Usually, this is caused by the absence of an absolute URL for the image. And absolute URL contains HTTPS and www, example "(http://www.app.wordfly.com/imagefolder/logo.png). Lotus Notes basically converts the image into Notes Rich Text and the image isn't present in the Notes Database. In other situations, and depending on the version of Lotus Notes, you may see a text representation of that image, example [Image]. This may be caused by a space in the image URL or image name. The easiest way to troubleshoot is to look at the image path and see if there are any breaks (spaces) in the image.
Strange boxes or lines in Lotus Notes
If you're seeing a border or line around your image, the majority of the time this is caused by using a gif image. Try removing the background on the gif or you can change the file type to jpg which will work much better.
Tables in Lotus Notes are overlooked
Lotus Notes tends to ignore table tags, nested table tags, and table tags that are not kept within another table. Try using one master table to constrain your entire email and add a padding of about 5 so that the email doesn't hit "compose" or "inbox". Note: Modern Editor emails use divs instead of tables for responsive design.
Lotus Notes disregards styles
You might notice text looking really huge or very small in Lotus Notes. This email client doesn't pay attention to CSS stylesheets.
Anchor tags usually don't work in Lotus Notes
Lotus Notes thinks the anchor tag href is a link to a document and tries to open it up; unfortunate, there's no work around for this behavior.