Sometimes our clients will have a problem that when sending emails via Salesforce message instead of Polish characters contains question mark ?.
This is caused by incorrect encoding the conversion of data from one form to another.
The solution to this issue is very simple, just change Email Encoding to Unicode (UTF-8) in the user settings.
In step 1 by clicking the gear icon in the upper right corner, select Setup, then in the browser (2) enter Users and go to configuration by clicking (3), then click Edit next to the user and on the right scrolling downwards in the Email Encoding field, select Unicode UTF-8 lists (4).
We hope that it was useful information for you and we encourage you to cooperate with ME PL in matching Salesforce solutions in your company.