How to notice incoming email exceeding max attachment size?

From time to time we receive emails from customers which exceed the "hard coded" max attachment size of 25 MB in Salesforce. I understand that this limit is actually not changeable, but how will our users get to know that such an email was refused by the Salesforce system so that they can react and e.g. contact the sender? Are those cases coming from "email-to-case" somehow "marked" or is it possible to access a log file via a flow or to use a filter setting that fits the requirement to list those cases (or emails instead) which have exceeded the max attachment size?

If anyone can suggest a solution, an example and/or screenshots would help, 

I think.

Thanks in advance for your support.

Frank