With the release of macOS 15.4, Apple introduced a bug in embedded WebKit, which is used in our application for viewing messages.
When the eM Client app tried to use WebKit on specific HTML/CSS code of the message, it caused a crash.
This issue unfortunately affected all versions of eM Client and of course, affects any other app using the same functions in the WebKit (for example the Eclipse IDE, whose programmers already reported the issue to Apple to resolve).
The issue was not resolved by the time Apple released 15.4.1, but thankfully we were already looking for a workaround, so the faulty process is NOT used in eM Client anymore and we released this update last Friday (April 25th).
So if you use macOS 15.4 or 15.4.1 and experience this crash, please check for update or manually install version 10.3.1720.