Add Support for Delivery Status Notification (DSN) in SMTP Client

[rustmailer]

Hi, I'm using the mail-send crate for sending emails in Rust and it works great for my needs so far. However, I noticed that there’s no direct support for configuring Delivery Status Notification (DSN) parameters, which are part of the SMTP protocol extension (RFC 3461). DSN is useful for receiving notifications about email delivery status (success, failure, or delay), and I’d love to see this feature added to the library.

DSN support depends on the SMTP server, but adding client-side configuration would make mail-send more versatile.

[mdecimus]

Hi, you can pass parameters to the MAIL FROM and RCPT TO commands, see here for instance:

mail-send/src/smtp/envelope.rs

Line 19 in 962518a

pub async fn mail_from(&mut self, addr: &str, params: &Parameters<'_>) -> crate::Result<()> {

[rustmailer]

@mdecimus thanks, I'll try it