Enum Tls

pub enum Tls {
    None,
    Opportunistic(TlsParameters),
    Required(TlsParameters),
    Wrapper(TlsParameters),
}

Specifies how to establish a TLS connection

TLDR: Use Tls::Wrapper or Tls::Required when connecting to a remote server, Tls::None when connecting to a local server.

Variants

None

Insecure (plaintext) connection only.

This option always uses a plaintext connection and should only be used for trusted local relays. It is highly discouraged for remote servers, as it exposes credentials and emails to potential interception.

Note: Servers requiring credentials or emails to be sent over TLS may reject connections when this option is used.

Opportunistic(TlsParameters)

Begin with a plaintext connection and attempt to use STARTTLS if available.

lettre will try to upgrade to a TLS-secured connection but will fall back to plaintext if the server does not support TLS. This option is provided for compatibility but is strongly discouraged, as it exposes connections to potential MITM (man-in-the-middle) attacks.

Warning: A malicious intermediary could intercept the STARTTLS flag, causing lettre to believe the server only supports plaintext connections.

Required(TlsParameters)

Begin with a plaintext connection and require STARTTLS for security.

lettre will upgrade plaintext TCP connections to TLS before transmitting any sensitive data. If the server does not support TLS, the connection attempt will fail, ensuring no credentials or emails are sent in plaintext.

Unlike Tls::Opportunistic, this option is secure against MITM attacks. For optimal security and performance, consider using Tls::Wrapper instead, as it requires fewer roundtrips to establish a secure connection.

Wrapper(TlsParameters)

Establish a connection wrapped in TLS from the start.

lettre connects to the server and immediately performs a TLS handshake. If the handshake fails, the connection attempt is aborted without transmitting any sensitive data.

This is the fastest and most secure option for establishing a connection.

Trait Implementations

impl Clone for Tls

fn clone(&self) -> Tls

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Debug for Tls

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.