We're using Thunderbird as an email client. Now I discovered that our emails are very large regarding file size. I figured out that the problem is indeed that the images in the email signature aren't properly linked, but they seem to be embedded automatically. When sending an email with an empty body to a colleague, the email is already 280kb. Her answer then includes my quoted signature and her own, wich already makes up 560kb...
I'd like all images to be linked. I couldn't find any resources on this topic, just the generic "embedded vs. linked images in emails". Does anyone have a clue why this is happening and what to do about it?
Maybe it's important mentioning that the linked images are HTTPS URIs, not HTTP. Also, all URIs point to files hosted on our WordPress-based website.
The signature is configured via the "Account Settings", it's obviously an HTML signature, and the HTML is pasted into the configuration window's "Signature Text" text field (see screenshot below).
All images are inserted using a standard SRC tag, like this:
<a href="https://example.com/"><img src="https://www.mydomain.de/wp-content/uploads/2015/01/image.png" alt="Image" width=50px; height=50px></a>