If this is happening to you, it's likely that the recipient reporting this is using Microsoft Outlook to receive their emails. Outlook does not recognize many CSS styles that are otherwise universally recognized, as you've noticed, and one of them is the "float" property that is used when aligning images using the text editor. In other words, the email likely shows up fine for most recipients, but for those recipients who view their emails in outlook, the 'float:left' property is ignored.

To account for this, you can also add an "align" attribute to the <img> tag by editing the HTML source code using the "HTML" button in the text editor. You will want to leave the "float" property there, as it is needed for modern email clients, but you can add the "align" property as well, making sure to add it as an HTML attribute instead of as inline CSS styling, like so:

Before:

<img style="float:none" src="example.jpg"> or <img style="text-align:center" src="example.jpg">

After:

<img style="float:none" src="example.jpg" align="middle"> or <img style="text-align:center" src="example.jpg" align="middle">