HTML-Markings (' ") appear in the title-line of emails

Summary

HTML-Markings (' ") appear in the title-line of emails that are sent by the system. (I tested if they appear if I send an email externally -to- my foodsharing-mailbox with signs like " but didn't get this bug. Also I don't get an email with this bug if I send myself an email -from- my foodsharing mailbox.)

What is the expected correct behavior?

The HTML-Markings (") should be displayed as the corresponding sign (").

Relevant error messages and/or screenshots

Possible fixes

None yet.