What is the difference between IsSecure and IsEncrypted?

[rklec]

I am using the ImapClient but this question may be answered more generally as it is applicable to all clients as far as I see.
There is IsSecure and IsEncrypted, but both have nearly the same doc/description, so what is actually the difference between them?
When should I use what (e.g. to check for an encrypted connection as in #387).

IsSecure:

MailKit/MailKit/Net/Imap/ImapClient.cs

Lines 684 to 693 in ff722f1

	/// <summary>
	/// Get whether or not the connection is secure (typically via SSL or TLS).
	/// </summary>
	/// <remarks>
	/// Gets whether or not the connection is secure (typically via SSL or TLS).
	/// </remarks>
	/// <value><c>true</c> if the connection is secure; otherwise, <c>false</c>.</value>
	public override bool IsSecure {
	get { return IsConnected && secure; }
	}

IsEncrypted:

MailKit/MailKit/Net/Imap/ImapClient.cs

Lines 695 to 704 in ff722f1

	/// <summary>
	/// Get whether or not the connection is encrypted (typically via SSL or TLS).
	/// </summary>
	/// <remarks>
	/// Gets whether or not the connection is encrypted (typically via SSL or TLS).
	/// </remarks>
	/// <value><c>true</c> if the connection is encrypted; otherwise, <c>false</c>.</value>
	public override bool IsEncrypted {
	get { return IsSecure && (engine.Stream.Stream is SslStream sslStream) && sslStream.IsEncrypted; }
	}

Only the code itself for IsEncrypted hints, it does more. So a connection is encrypted when it is (also) secure? Note for my language understanding thus sounds weird, as usually, I'd say a connection is secure, when it is encrypted (and maybe authenticated etc.). So "security" as a concept involves more than just encryption. But that's just my personal opinion here.
However, this only seems to apply to the ImapClient. So what is the difference, in human terms?

[jstedfast]

The IsSecure property was added first and all it means is that an SSL/TLS connection has been made.

IsEncrypted was added years later and returns true if the SslStream's IsEncrypted property is true.