(1) Which email providers are supported?
(2) What is a valid security certificate?
Valid security certificates are officially signed (not self signed) and have matching a host name.
(3) Which permissions are needed and why?
The low priority status bar notification shows the number of pending operations, which can be:
(5) What happens if a message could not be sent?
If a message could not be sent, it will be placed in the drafts folder again.
If you have another question, you can use this forum.