What is the nosend attribute?
It is usually found in an image tag and looks like this: <img nosend="1"/>. It is generally discovered by inquisitive developers by examining a “right-click > view source” on HTML email messages in Outlook. Google generally provides more questions than answers, so I thought I would include what I believe to be true about mysterious nosend attribute.
The nosend attribute is an undocumented and non-standard HTML attributed used by Outlook (go figure) to decide how to handle the URLs for images included in HTML email.
Without the nosend attribute (or with nosend="0"), Outlook has a few different behaviors. If you’re all set up to send the HTML email using Outlook, if you copy the images to your stationery folder and reference them in the HTML with relative urls (without the http://), when you send the email Outlook will attach the images to the email and rewrite the links to reference the attached images. Recipients get an email with lots of image attachments, and the references usually break when people forward or reply to the email.
If you use absolute urls (with the http://), Outlook usually doesn’t rewrite the references when you send the email, but if they foward/reply, Outlook will attach the images as above, then the next forward/reply usually breaks them.
With the nosend="1" attribute on your image elements, and using absolute URLs, Outlook will not rewrite your image URLs. There’s an almost infinite number of ways users can send, attach, include, reply, and forward these emails so it’s still possible for users to break the URLs. But as far as I can tell, the nosend attribute tells Outlook not to mess with the URLs.
BTW, if you’re using CSS in HTML email, Outlook generally leaves image URLs in stylesheets or inline style attributes alone.