web.config file
Configuration can be performed using standard .NET tools
(<mailSettings>),
or by the mailSettings element in the <appSettings> section.
The json-text format for <appSettings> is identical to the standard .NET settings format.
Please note! If the delivery method 'SpecifiedPickupDirectory' is set
(used for testing, without actually sending a message), then you must obligatorily specify
the folder where test messages will be placed (pickupDirectoryLocation).
Example of configuring via system.net