Profile Pictures in E-Mails do not contain picture if profile picture name contains spaces or umlauts

Confluence sometimes sends E-mails to users, e.g. when watching pages.
If the profile picture of a user contains only ascii characters and no spaces, the email contains the user profile picture.
When the profile picture contains a space or e.g. german umlauts, the profile picture is NOT part of the emails sent from Confluence.

Attached you find an example for a user which has a profile picture with a german umlaut