I wonder if anyone knows that Lotus notes does not support any urls embedded on a button?
I understand the rendering may not appear correctly but URLs?
Or is it because of the button cannot display properly?
Please help as I have got a client on my back...
What do you mean by "button"? <button> or <input type="button"> or <a href=""><img></a>. Seems like the latter would be the most reliable.
The way to answer your question is to test it. Create a test email with everything that you want to know if it works or not and send it to someone with Lotus Notes and find out what breaks and what doesn't.
As Derek mentioned, an image that is linked to a URL would be your best bet, and should work fine in Lotus Notes.