Emails lost when enabled "Use a different 'From' address for email-notifications in this category"

Problem:

When you specify a different "From" email address for a certain ticket category, it may happen that email notifications don't get sent when users reply to tickets in that category, although the email works fine when the Use a different "from" address for email-notifications in this category option is cleared.

Solution:

To use email addresses different from the default one (set on the Email settings screen), make sure that your SMTP server allows sending messages with the email address you provide in the category settings. To do so, you may have to add the "send as" privileges for the "from" addresses that you want to use for your ticket categories.