Optimal html email width
500 - 600 pixels.
Probably the lowest possible screen resolution these days is 800x600 so the email should fit into 800 pizels. But you’ll have to substract browser/email client scroll bar and border width from that number so probably available width is about 750 pixels. But to play it safe most folks recommend 500 to 600 pizels. This way user is guaranteed to see your email message without ugly horizontal scrolling.
BTW in my current Tumblr layout the width is 450 pixels.
