What are Linked Images and What are Inline Images?
Linked Images: Images as URLs
If you send the images in your message as linked images, then the message itself will only contain URL references to the images which themselves are stored on a web server. The actual image data will not be part of the message and will therefore also not be included in the message data that is sent from Maestro, via the email servers, to the recipient's email client.
When the recipient's email client displays the message, it will then load the images from their locations on the web server "just-in-time", at the moment the message is being displayed.
Advantages: The message itself remains relatively small, since it does not contain the image data, but only a textual reference. In comparison, the image data is always much larger than such a reference. So a message with linked images is delivered more quickly and takes up less bandwidth.
Disadvantages: Many modern email clients do initially not display linked
images when the message is first opened by the recipient. They leave it up to the recipient to decide if he
wants to see linked images or not. So the actual images are only loaded and displayed when, and if, the
user says so. Or linked images can also fail to load if the recipient is viewing the email while he
is offline (for example on a laptop that is currently not connected to the Internet).
In both cases, your message may appear broken or ugly while the images are not displayed. And if the images contain an important part of your message, the message may even appear nonsensical without them.
Inline Images: Images as Attachments
If you send the images in your message as inline images, then the message will contain the actual image data (as special attachments). This means that the image data will be part of the message data which is sent from Maestro, via the email servers, to the recipient's email client.
When the recipient's email client displays the message, it already has all the image data right there in the message and uses it to display the images.
Advantages: Email clients usually do not block inline images but display them right away (although some clients may still block them until the user opts to display them). In addition, inline images are displayed without problems even if the recipient is viewing the email while he is offline (for example on a laptop that is currently not connected to the Internet). Therefore, with inline images you have a good chance that your message will appear exactly as intended, with all images in place.
Disadvantages: Including the image data in the message makes the message larger.
And a copy of the data of each inline image will be included in each individual message, for each individual
recipient. Especially if you have very many recipients, this "multiplication" of the image data can take
up a considerable amount of your delivery bandwidth, slowing down delivery.
Another disadvantage is that many email clients display inline images not only in the message itself, but also in the list of attachments. Depending on what images you have, this effect may be undesired.
When using content conditions with images (either image widgets or standard HTML images), inline images also have the disadvantage that the image attachments are always included in their entirety for all recipients. I.e., even for a recipient where the content condition may hide a given image, the matching image attachment is still included in the message, even though it is actually unnecessary.
Linked or Inline Images - Help me choose the right option!
When trying to decide if you should send the images in your messages as a linked or an inline images, there is one main question you have to answer for yourself:
What is most important to me?
The images shall be displayed to the recipients with as few problems as possible!
This would be important if the images are essential to your message, for example if the message would look very ugly if the images are not being displayed, or if the images themselves contain important parts of the message.
→ You should include images as inline images, so that they are (likely) not blocked by the recipients' email clients.
The message size shall be as small as possible!
This would be important if you have very many recipients and/or many images in the message, and you do not want to impact the delivery time of the message negatively by the higher amount of network bandwidth that would be consumed by the image data.
→ You should include images as linked images, so that they do not require any of your bandwidth.
Images hidden by content conditions shall not be included in the message!
This would be important if you use content conditions on image widgets or to selectively hide generic HTML images. With inline images, the message always includes all image attachments, even of those images that are actually hidden for the recipient by a content condition.
→ You should include images as linked images, so that there are no superfluous attachments if images are hidden by conditions.
The images shall not appear as attachments!
This would be important if you do not like the fact that many email clients display inline images also as attachments (in addition to displaying them in the message itself). Especially if you also include attachments of your own, and you do not want your attachments to "get lost" among the list of image attachments.
→ You should include images as linked images, so that they do not show up as attachments.