[BUG] Email through Starttls not working

[zaggash]

Describe the bug
Using the CLI to test the smtp and working on port 587 STARTTL is not working when it is wokring fine with others applications.

It throws me the following error:

2024-04-02T16:55:34.298682303+00:00  ERROR    🚨 [error]: TLS alert received: AlertMessagePayload {
    level: Fatal,
    description: ProtocolVersion,
} | log.target: "rustls::conn" | log.module_path: "rustls::conn" | log.file: "/__w/lldap/lldap/${GITHUB_WORKSPACE}/.cargo/registry/src/index.crates.io-6f17d22bba15001f/rustls-0.20.8/src/conn.rs" | log.line: 1327
Error: Could not send email: {:#}

Caused by:
    0: Connection error: Connection error: received fatal alert: ProtocolVersion
    1: Connection error: received fatal alert: ProtocolVersion
    2: received fatal alert: ProtocolVersion

smtp_options: MailOptions {
        enable_password_reset: true,
        from: Some(
            Mailbox {
                name: None,
                email: Address {
                    serialized: "ldap@mydomain.tld",
                    at_start: 4,
                },
            },
        ),
        reply_to: Some(
            Mailbox {
                name: None,
                email: Address {
                    serialized: "noreply@mydomain.tld",
                    at_start: 7,
                },
            },
        ),
        server: "smtp.server.tld",
        port: 587,
        user: "userlogin@domain.tld",
        password: ***SECRET***,
        smtp_encryption: StartTls,
        tls_required: None,

To Reproduce
Steps to reproduce the behavior:

1. docker exec in the lldap container
2. Setup your credentials and smtp settings for /app/lldap send_test_email
3. Set the --smtp-encryption to STARTTLS
4. See error

Expected behavior
The email should be sent.

However, if I use TLS on port 465 it is working fine.

[nitnelave]

That sounds more like an issue with lettre, the email library we're using. Although out of curiosity, why use starttls when TLS works? It's simply superior.

[zaggash]

I didn't know how SMTP encryption worked.
I figured I better use TLS after a bit of research.
However, I wanted to report for others.