currently de:wp sends mails like this:
Micha hinterließ eine Nachricht auf deiner Diskussionsseite.
Nachricht ansehen Micha Änderungen ansehen
on every change micha makes on the talk page. it would be better that the notification mail is coupled onto the global notification indicator, and is deferred by, say, an hour or so. this would then avoid double notification mails and inform about everything.
Emails are being sent only once until you visit the page again. If you visit it, the email is being sent again on its first following change...
This applies to watchlist emails, but the email here is an Echo notification email.
You can change it to send you daily batches ("Tägliche Zusammenfassung der Benachrichtigungen") at https://de.wikipedia.org/wiki/Spezial:Einstellungen#mw-prefsection-echo .
I put Declined before since we removed a similar feature, but DannyB pointed out Invalid is better since there is a close-enough feature you can still use.