Most email clients block images in emails by default mainly for security reasons. Specifically, this feature prevents recipients from:
Downloading malicious content or images that could lead to malicious websites.
Providing analytics to senders about the recipient’s email address, geographical location, IP address etc.
Downloading large content in size when using a low-bandwidth connection.
Viewing potentially offensive material
Every email client treats image blocking differently so this is a situation that can not be controlled by the sender. Normally, when the recipient whitelists an email address, the email client will automatically download the images next time it receives an email from the specific sender.
With Outlook OWA, you can add a sender to the trusted list by clicking on the link below:
In Outlook 2013/2016, to add an address to the Safe Sender list, you need to do the following:
On the Home tab, click Junk, and then click Never Block sender.