After upgrade our platform from Moodle 4.2 to Moodle 4.3.3+ (Boost union theme), the icon of the file type in the attached files of the posts, it is displayed with a big size (372x372px aprox) in the email notification. 

It seems that the size in not defined when the email template generates the html code to send:

<img data-imagetype="External" src="https://contoso.com/theme/image.php/boost_union/core/xxxxxxxx/f/image" class="x_icon x_icon" alt="Imatge (JPEG)" title="Imatge (JPEG)">

By the other side, the user picture size is correct: 

<img data-imagetype="External" src="https://contoso.com/pluginfile.php/xxxxx/user/icon/boost_union/f2?rev=yyyyyy" class="x_userpicture" width="35" height="35" alt="aaaaa" title="aaaaa">