Embedded vs hosted images in email signatures
To add imagery to an HTML email signature, you have two options available to you. You can either add a logo/image by embedding it directly into the signature or hosting it externally and linking to it.
The vast majority of email clients display logos/images in an email signature without any major issues, so there might not appear to be much difference between using the two formats. However, there are benefits to choosing one method over the other.
If you want a logo/imagery to appear without having to click a ‘Download Images’ button, we recommend embedding it all within the email signature. This is when an image is attached to an email and referenced using a Content-ID (HTML image tags).
A standard Content-ID will look like this:
<img src="cid:myimagecid" />
When an email client refers to these images, they will all be displayed automatically. This is because they are referenced in the source of the message.
However, embedded images will slightly increase the size of your emails and there is a slight risk that they will appear as separate attachments in some email clients. There are also known issues with images being stripped out of emails and increasing in size on iOS devices e.g. iPhone and iPad.
If you don't want to run the risk of email signature imagery appearing as attachments, we recommend saving and hosting your logo/images on a web server. They will then be referenced in the email using a web URL. This is known as hosting or linking images:
A hosted/linked image would typically look like this:
<img src="https://a8b03ffbc00ed4da54a1-0c6684360696717b63d89dbc0edb802c.ssl.cf1.rackcdn.com/exclaimer-logo_178x36.png" />
By doing this, your images are never a physical part of the email. Instead, they are essentially downloaded into the message every time it is viewed, making the email file size smaller.
In some cases, a recipient may need to manually click a 'Download Images' button for the email signature imagery to be displayed. This is a way of protecting the recipient against possible viruses.
Which option should I choose?
You need to consider how your customers/clients view the emails you send them. If a large percentage use email clients like Outlook, then embedded images are probably the way to go. If, however, you know that a lot of recipients will view your emails on mobile devices, we recommend you use hosted imagery.