send notifications only daily (maybe as summary)

[flosse]

Give the user the choice, eather to get daily mail reports or a notification per Entry.

• Don't send the notification immediatly, but delay it at least for one hour or even for one day, otherwise, you might send too many mails when people again and again change entries.

The mail contains changed entries with:

• title
• link
• city

Footer: Link to unsubscribe (see #45)

All new informations should be bold, all deleted informations (especially tags) should be ~~scratched out~~

[uklotzde]

Mails should also not be sent while processing a request! This delays the response after the actual task has already been finished and the request may time out if anything goes wrong.

All mail and subscription processing has to be done separately by a background thread/task. Either queuing pending tasks in-memory or by using a temporary table.