I noticed that almost all email messages I get do not embed images, but link them from the http instead (and they get blocked by default of course). I'm sending HTML email for my service and can easily embed images to create better visual experience. Is there particular reason not do so? Why everybody else is linking instead of embedding?
Because by embedding the images in the email, the email size gets a lot larger, uses more bandwidth for you to send it, and more for them to receive it. If the images are important to the email's purpose then embed them, if they are to just make it look good then link them.
A few possible considerations:
- If you're sending a lot of email, the amount of time to send them all out is going to be an important consideration. Including images in the email hugely multiplies its size compared to plain text, so each email will take many times longer to send.
- If you embed the images, it guarantees that for every email you send, you're going to be using the bandwidth for those images. If you're sending a mass email and some of them don't get read, that was wasted bandwidth. With linked images you only have to use the bandwidth when someone actually opens the email.
- If you embed the images, as soon as you send the email, you're committed. If you want to make a quick change to one of the images and you had linked it, you'll still be able to.
Many mass email services also link the images for another reason: it allows them to track who has opened the email.
Interestingly, I've noticed GMail marking images as spam if they include links to images. The same email with an image embedded does not trip gmail's spam filter.
Here's a post on the topic where someone else noticed the same thing:
http://blog.whitesites.com/Trick-to-getting-past-Gmail-Spam-Filters__634486187705400390_blog.htm
linking naturally saves bandwidth which if your service legitimately sends many emails is certainly an important consideration. I agree though embedding images does create a better user experience. I would embed images if you know your demographic aren't going to filter the images which IMHO looks worse than linked images.
Another consideration is the use of the images. Are you going to include them as incidental to the content ie. could they not be included as links at the end? In your case I suspect not, so we're back to bandwidth and filtration considerations.
Hope this helps.
来源：https://stackoverflow.com/questions/2429358/images-in-email-link-or-embed