Files
Stalwart/crates/smtp/src/inbound/data.rs

926 lines
34 KiB
Rust

/*
* SPDX-FileCopyrightText: 2020 Stalwart Labs Ltd <hello@stalw.art>
*
* SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-SEL
*/
use std::{
borrow::Cow,
time::{Duration, Instant, SystemTime},
};
use common::{
config::{
smtp::{auth::VerifyStrategy, session::Stage},
spamfilter::SpamFilterAction,
},
listener::SessionStream,
psl,
scripts::ScriptModification,
};
use mail_auth::{
AuthenticatedMessage, AuthenticationResults, DkimResult, DmarcResult, ReceivedSpf,
common::{headers::HeaderWriter, verify::VerifySignature},
dmarc::{self, verify::DmarcParameters},
};
use mail_builder::headers::{date::Date, message_id::generate_message_id_header};
use mail_parser::MessageParser;
use sieve::runtime::Variable;
use smtp_proto::{
MAIL_BY_RETURN, RCPT_NOTIFY_DELAY, RCPT_NOTIFY_FAILURE, RCPT_NOTIFY_NEVER, RCPT_NOTIFY_SUCCESS,
};
use store::write::now;
use trc::SmtpEvent;
use utils::config::Rate;
use crate::{
core::{Session, SessionAddress, State},
inbound::milter::Modification,
queue::{self, Message, MessageSource, QueueEnvelope, Schedule, quota::HasQueueQuota},
reporting::analysis::AnalyzeReport,
scripts::ScriptResult,
};
use super::{ArcSeal, AuthResult, DkimSign};
impl<T: SessionStream> Session<T> {
pub async fn queue_message(&mut self) -> Cow<'static, [u8]> {
// Parse message
let raw_message = std::mem::take(&mut self.data.message);
let parsed_message = match MessageParser::new()
.parse(&raw_message)
.filter(|p| p.headers().iter().any(|h| !h.name.is_other()))
{
Some(parsed_message) => parsed_message,
None => {
trc::event!(
Smtp(SmtpEvent::MessageParseFailed),
SpanId = self.data.session_id,
);
return (&b"550 5.7.7 Failed to parse message.\r\n"[..]).into();
}
};
// Authenticate message
let auth_message = AuthenticatedMessage::from_parsed(
&parsed_message,
self.server.core.smtp.mail_auth.dkim.strict,
);
let has_date_header = auth_message.has_date_header();
let has_message_id_header = auth_message.has_message_id_header();
// Loop detection
let dc = &self.server.core.smtp.session.data;
let ac = &self.server.core.smtp.mail_auth;
let rc = &self.server.core.smtp.report;
if auth_message.received_headers_count()
> self
.server
.eval_if(&dc.max_received_headers, self, self.data.session_id)
.await
.unwrap_or(50)
{
trc::event!(
Smtp(SmtpEvent::LoopDetected),
SpanId = self.data.session_id,
Total = auth_message.received_headers_count(),
);
return (&b"450 4.4.6 Too many Received headers. Possible loop detected.\r\n"[..])
.into();
}
// Verify DKIM
let dkim = self
.server
.eval_if(&ac.dkim.verify, self, self.data.session_id)
.await
.unwrap_or(VerifyStrategy::Relaxed);
let dmarc = self
.server
.eval_if(&ac.dmarc.verify, self, self.data.session_id)
.await
.unwrap_or(VerifyStrategy::Relaxed);
let dkim_output = if dkim.verify() || dmarc.verify() {
let time = Instant::now();
let dkim_output = self
.server
.core
.smtp
.resolvers
.dns
.verify_dkim(self.server.inner.cache.build_auth_parameters(&auth_message))
.await;
let pass = dkim_output
.iter()
.any(|d| matches!(d.result(), DkimResult::Pass));
let strict = dkim.is_strict();
let rejected = strict && !pass;
// Send reports for failed signatures
if let Some(rate) = self
.server
.eval_if::<Rate, _>(&rc.dkim.send, self, self.data.session_id)
.await
{
for output in &dkim_output {
if let Some(rcpt) = output.failure_report_addr() {
self.send_dkim_report(rcpt, &auth_message, &rate, rejected, output)
.await;
}
}
}
trc::event!(
Smtp(if pass {
SmtpEvent::DkimPass
} else {
SmtpEvent::DkimFail
}),
SpanId = self.data.session_id,
Strict = strict,
Result = dkim_output.iter().map(trc::Error::from).collect::<Vec<_>>(),
Elapsed = time.elapsed(),
);
if rejected {
// 'Strict' mode violates the advice of Section 6.1 of RFC6376
return if dkim_output
.iter()
.any(|d| matches!(d.result(), DkimResult::TempError(_)))
{
(&b"451 4.7.20 No passing DKIM signatures found.\r\n"[..]).into()
} else {
(&b"550 5.7.20 No passing DKIM signatures found.\r\n"[..]).into()
};
}
dkim_output
} else {
vec![]
};
// Verify ARC
let arc = self
.server
.eval_if(&ac.arc.verify, self, self.data.session_id)
.await
.unwrap_or(VerifyStrategy::Relaxed);
let arc_sealer = self
.server
.eval_if::<String, _>(&ac.arc.seal, self, self.data.session_id)
.await
.and_then(|name| self.server.get_arc_sealer(&name, self.data.session_id));
let arc_output = if arc.verify() || arc_sealer.is_some() {
let time = Instant::now();
let arc_output = self
.server
.core
.smtp
.resolvers
.dns
.verify_arc(self.server.inner.cache.build_auth_parameters(&auth_message))
.await;
let strict = arc.is_strict();
let pass = matches!(arc_output.result(), DkimResult::Pass | DkimResult::None);
trc::event!(
Smtp(if pass {
SmtpEvent::ArcPass
} else {
SmtpEvent::ArcFail
}),
SpanId = self.data.session_id,
Strict = strict,
Result = trc::Error::from(arc_output.result()),
Elapsed = time.elapsed(),
);
if strict && !pass {
return if matches!(arc_output.result(), DkimResult::TempError(_)) {
(&b"451 4.7.29 ARC validation failed.\r\n"[..]).into()
} else {
(&b"550 5.7.29 ARC validation failed.\r\n"[..]).into()
};
}
arc_output.into()
} else {
None
};
// Build authentication results header
let mail_from = self.data.mail_from.as_ref().unwrap();
let mut auth_results = AuthenticationResults::new(&self.hostname);
if !dkim_output.is_empty() {
auth_results = auth_results.with_dkim_results(&dkim_output, auth_message.from())
}
if let Some(spf_ehlo) = &self.data.spf_ehlo {
auth_results = auth_results.with_spf_ehlo_result(
spf_ehlo,
self.data.remote_ip,
&self.data.helo_domain,
);
}
if let Some(spf_mail_from) = &self.data.spf_mail_from {
auth_results = auth_results.with_spf_mailfrom_result(
spf_mail_from,
self.data.remote_ip,
&mail_from.address,
&self.data.helo_domain,
);
}
if let Some(iprev) = &self.data.iprev {
auth_results = auth_results.with_iprev_result(iprev, self.data.remote_ip);
}
// Verify DMARC
let is_report = self.is_report();
let (dmarc_result, dmarc_policy) = match &self.data.spf_mail_from {
Some(spf_output) if dmarc.verify() => {
let time = Instant::now();
let dmarc_output =
self.server
.core
.smtp
.resolvers
.dns
.verify_dmarc(self.server.inner.cache.build_auth_parameters(
DmarcParameters {
message: &auth_message,
dkim_output: &dkim_output,
rfc5321_mail_from_domain: if !mail_from.domain.is_empty() {
&mail_from.domain
} else {
&self.data.helo_domain
},
spf_output,
domain_suffix_fn: |domain| {
psl::domain_str(domain).unwrap_or(domain)
},
},
))
.await;
let pass = matches!(dmarc_output.spf_result(), DmarcResult::Pass)
|| matches!(dmarc_output.dkim_result(), DmarcResult::Pass);
let strict = dmarc.is_strict();
let rejected = strict && dmarc_output.policy() == dmarc::Policy::Reject && !pass;
let is_temp_fail = rejected
&& matches!(dmarc_output.spf_result(), DmarcResult::TempError(_))
|| matches!(dmarc_output.dkim_result(), DmarcResult::TempError(_));
// Add to DMARC output to the Authentication-Results header
auth_results = auth_results.with_dmarc_result(&dmarc_output);
let dmarc_result = if pass {
DmarcResult::Pass
} else if dmarc_output.spf_result() != &DmarcResult::None {
dmarc_output.spf_result().clone()
} else if dmarc_output.dkim_result() != &DmarcResult::None {
dmarc_output.dkim_result().clone()
} else {
DmarcResult::None
};
let dmarc_policy = dmarc_output.policy();
trc::event!(
Smtp(if pass {
SmtpEvent::DmarcPass
} else {
SmtpEvent::DmarcFail
}),
SpanId = self.data.session_id,
Strict = strict,
Domain = dmarc_output.domain().to_string(),
Policy = dmarc_policy.to_string(),
Result = trc::Error::from(&dmarc_result),
Elapsed = time.elapsed(),
);
// Send DMARC report
if dmarc_output.requested_reports() && !is_report {
self.send_dmarc_report(
&auth_message,
&auth_results,
rejected,
dmarc_output,
&dkim_output,
&arc_output,
)
.await;
}
if rejected {
return if is_temp_fail {
(&b"451 4.7.1 Email temporarily rejected per DMARC policy.\r\n"[..]).into()
} else {
(&b"550 5.7.1 Email rejected per DMARC policy.\r\n"[..]).into()
};
}
(dmarc_result.into(), dmarc_policy.into())
}
_ => (None, None),
};
// Analyze reports
if is_report {
if !rc.analysis.forward {
self.server.analyze_report(
mail_parser::Message {
html_body: parsed_message.html_body,
text_body: parsed_message.text_body,
attachments: parsed_message.attachments,
parts: parsed_message
.parts
.into_iter()
.map(|p| p.into_owned())
.collect(),
raw_message: b"".into(),
},
self.data.session_id,
);
self.data.messages_sent += 1;
return (b"250 2.0.0 Message queued for delivery.\r\n"[..]).into();
} else {
self.server.analyze_report(
mail_parser::Message {
html_body: parsed_message.html_body.clone(),
text_body: parsed_message.text_body.clone(),
attachments: parsed_message.attachments.clone(),
parts: parsed_message
.parts
.iter()
.map(|p| p.clone().into_owned())
.collect(),
raw_message: b"".into(),
},
self.data.session_id,
);
}
}
// Add Received header
let message_id = self.server.inner.data.queue_id_gen.generate();
let mut headers = Vec::with_capacity(64);
if self
.server
.eval_if(&dc.add_received, self, self.data.session_id)
.await
.unwrap_or(true)
{
self.write_received(&mut headers, message_id)
}
// Add authentication results header
if self
.server
.eval_if(&dc.add_auth_results, self, self.data.session_id)
.await
.unwrap_or(true)
{
auth_results.write_header(&mut headers);
}
// Add Received-SPF header
if let Some(spf_output) = &self.data.spf_mail_from {
if self
.server
.eval_if(&dc.add_received_spf, self, self.data.session_id)
.await
.unwrap_or(true)
{
ReceivedSpf::new(
spf_output,
self.data.remote_ip,
&self.data.helo_domain,
&mail_from.address_lcase,
&self.hostname,
)
.write_header(&mut headers);
}
}
// ARC Seal
if let (Some(arc_sealer), Some(arc_output)) = (arc_sealer, &arc_output) {
if !dkim_output.is_empty() && arc_output.can_be_sealed() {
match arc_sealer.seal(&auth_message, &auth_results, arc_output) {
Ok(set) => {
set.write_header(&mut headers);
}
Err(err) => {
trc::error!(
trc::Error::from(err)
.span_id(self.data.session_id)
.details("Failed to ARC seal message")
);
}
}
}
}
// Run SPAM filter
if self.server.core.spam.enabled
&& self
.server
.eval_if(&dc.spam_filter, self, self.data.session_id)
.await
.unwrap_or(true)
{
match self
.spam_classify(
&parsed_message,
&dkim_output,
(&arc_output).into(),
dmarc_result.as_ref(),
dmarc_policy.as_ref(),
)
.await
{
SpamFilterAction::Allow(spam_headers) => {
if !spam_headers.is_empty() {
headers.extend_from_slice(spam_headers.as_bytes());
}
}
SpamFilterAction::Discard => {
self.data.messages_sent += 1;
return (b"250 2.0.0 Message queued for delivery.\r\n"[..]).into();
}
SpamFilterAction::Reject => {
self.data.messages_sent += 1;
return (b"550 5.7.1 Message rejected due to excessive spam score.\r\n"[..])
.into();
}
}
}
// Run Milter filters
let mut modifications = Vec::new();
match self.run_milters(Stage::Data, (&auth_message).into()).await {
Ok(modifications_) => {
if !modifications_.is_empty() {
modifications = modifications_;
}
}
Err(response) => {
return response.into_bytes();
}
};
// Run MTA Hooks
match self
.run_mta_hooks(Stage::Data, (&auth_message).into(), message_id.into())
.await
{
Ok(modifications_) => {
if !modifications_.is_empty() {
modifications.retain(|m| !matches!(m, Modification::ReplaceBody { .. }));
modifications.extend(modifications_);
}
}
Err(response) => {
return response.into_bytes();
}
};
// Apply modifications
let mut edited_message = if !modifications.is_empty() {
self.data
.apply_milter_modifications(modifications, &auth_message)
} else {
None
};
// Sieve filtering
if let Some((script, script_id)) = self
.server
.eval_if::<String, _>(&dc.script, self, self.data.session_id)
.await
.and_then(|name| {
self.server
.get_trusted_sieve_script(&name, self.data.session_id)
.map(|s| (s, name))
})
{
let params = self
.build_script_parameters("data")
.with_auth_headers(&headers)
.set_variable(
"arc.result",
arc_output
.as_ref()
.map(|a| a.result().as_str())
.unwrap_or_default(),
)
.set_variable(
"dkim.result",
dkim_output
.iter()
.find(|r| matches!(r.result(), DkimResult::Pass))
.or_else(|| dkim_output.first())
.map(|r| r.result().as_str())
.unwrap_or_default(),
)
.set_variable(
"dkim.domains",
dkim_output
.iter()
.filter_map(|r| {
if matches!(r.result(), DkimResult::Pass) {
r.signature()
.map(|s| Variable::from(s.domain().to_lowercase()))
} else {
None
}
})
.collect::<Vec<_>>(),
)
.set_variable(
"dmarc.result",
dmarc_result
.as_ref()
.map(|a| a.as_str())
.unwrap_or_default(),
)
.set_variable(
"dmarc.policy",
dmarc_policy
.as_ref()
.map(|a| a.as_str())
.unwrap_or_default(),
)
.with_message(parsed_message);
let modifications = match self.run_script(script_id, script.clone(), params).await {
ScriptResult::Accept { modifications } => modifications,
ScriptResult::Replace {
message,
modifications,
} => {
edited_message = message.into();
modifications
}
ScriptResult::Reject(message) => {
return message.as_bytes().to_vec().into();
}
ScriptResult::Discard => {
return (b"250 2.0.0 Message queued for delivery.\r\n"[..]).into();
}
};
// Apply modifications
for modification in modifications {
match modification {
ScriptModification::AddHeader { name, value } => {
headers.extend_from_slice(name.as_bytes());
headers.extend_from_slice(b": ");
headers.extend_from_slice(value.as_bytes());
if !value.ends_with('\n') {
headers.extend_from_slice(b"\r\n");
}
}
ScriptModification::SetEnvelope { name, value } => {
self.data.apply_envelope_modification(name, value);
}
}
}
}
// Build message
let mail_from = self.data.mail_from.clone().unwrap();
let rcpt_to = std::mem::take(&mut self.data.rcpt_to);
let mut message = self
.build_message(mail_from, rcpt_to, message_id, self.data.session_id)
.await;
// Add Return-Path
if self
.server
.eval_if(&dc.add_return_path, self, self.data.session_id)
.await
.unwrap_or(true)
{
headers.extend_from_slice(b"Return-Path: <");
headers.extend_from_slice(message.return_path.as_bytes());
headers.extend_from_slice(b">\r\n");
}
// Add any missing headers
if !has_date_header
&& self
.server
.eval_if(&dc.add_date, self, self.data.session_id)
.await
.unwrap_or(true)
{
headers.extend_from_slice(b"Date: ");
headers.extend_from_slice(Date::now().to_rfc822().as_bytes());
headers.extend_from_slice(b"\r\n");
}
if !has_message_id_header
&& self
.server
.eval_if(&dc.add_message_id, self, self.data.session_id)
.await
.unwrap_or(true)
{
headers.extend_from_slice(b"Message-ID: ");
let _ = generate_message_id_header(&mut headers, &self.hostname);
headers.extend_from_slice(b"\r\n");
}
// DKIM sign
let raw_message = edited_message.as_deref().unwrap_or(raw_message.as_slice());
for signer in self
.server
.eval_if::<Vec<String>, _>(&ac.dkim.sign, self, self.data.session_id)
.await
.unwrap_or_default()
{
if let Some(signer) = self.server.get_dkim_signer(&signer, self.data.session_id) {
match signer.sign_chained(&[headers.as_ref(), raw_message]) {
Ok(signature) => {
signature.write_header(&mut headers);
}
Err(err) => {
trc::error!(
trc::Error::from(err)
.span_id(self.data.session_id)
.details("Failed to DKIM sign message")
);
}
}
}
}
// Update size
message.size = (raw_message.len() + headers.len()) as u64;
// Verify queue quota
if self.server.has_quota(&mut message).await {
// Prepare webhook event
let queue_id = message.queue_id;
// Queue message
let source = if !self.is_authenticated() {
MessageSource::Unauthenticated
} else {
MessageSource::Authenticated
};
if message
.queue(
Some(&headers),
raw_message,
self.data.session_id,
&self.server,
source,
)
.await
{
self.state = State::Accepted(queue_id);
self.data.messages_sent += 1;
(b"250 2.0.0 Message queued for delivery.\r\n"[..]).into()
} else {
(b"451 4.3.5 Unable to accept message at this time.\r\n"[..]).into()
}
} else {
(b"452 4.3.1 Mail system full, try again later.\r\n"[..]).into()
}
}
pub async fn build_message(
&self,
mail_from: SessionAddress,
mut rcpt_to: Vec<SessionAddress>,
queue_id: u64,
span_id: u64,
) -> Message {
// Build message
let created = SystemTime::now()
.duration_since(SystemTime::UNIX_EPOCH)
.map_or(0, |d| d.as_secs());
let mut message = Message {
queue_id,
span_id,
created,
return_path: mail_from.address,
return_path_lcase: mail_from.address_lcase,
return_path_domain: mail_from.domain,
recipients: Vec::with_capacity(rcpt_to.len()),
domains: Vec::with_capacity(3),
flags: mail_from.flags,
priority: self.data.priority,
size: 0,
env_id: mail_from.dsn_info,
blob_hash: Default::default(),
quota_keys: Vec::new(),
};
// Add recipients
let future_release = Duration::from_secs(self.data.future_release);
rcpt_to.sort_unstable();
for rcpt in rcpt_to {
if message
.domains
.last()
.is_none_or(|d| d.domain != rcpt.domain)
{
let rcpt_idx = message.domains.len();
message.domains.push(queue::Domain {
retry: Schedule::now(),
notify: Schedule::now(),
expires: 0,
status: queue::Status::Scheduled,
domain: rcpt.domain,
});
let envelope = QueueEnvelope::new(&message, rcpt_idx);
// Set next retry time
let retry = if self.data.future_release == 0 {
queue::Schedule::now()
} else {
queue::Schedule::later(future_release)
};
// Set expiration and notification times
let config = &self.server.core.smtp.queue;
let (num_intervals, next_notify) = self
.server
.eval_if::<Vec<Duration>, _>(&config.notify, &envelope, self.data.session_id)
.await
.and_then(|v| (v.len(), v.into_iter().next()?).into())
.unwrap_or_else(|| (1, Duration::from_secs(86400)));
let (notify, expires) = if self.data.delivery_by == 0 {
(
queue::Schedule::later(future_release + next_notify),
now()
+ future_release.as_secs()
+ self
.server
.eval_if(&config.expire, &envelope, self.data.session_id)
.await
.unwrap_or_else(|| Duration::from_secs(5 * 86400))
.as_secs(),
)
} else if (message.flags & MAIL_BY_RETURN) != 0 {
(
queue::Schedule::later(future_release + next_notify),
now() + self.data.delivery_by as u64,
)
} else {
let expire = self
.server
.eval_if(&config.expire, &envelope, self.data.session_id)
.await
.unwrap_or_else(|| Duration::from_secs(5 * 86400));
let expire_secs = expire.as_secs();
let notify = if self.data.delivery_by.is_positive() {
let notify_at = self.data.delivery_by as u64;
if expire_secs > notify_at {
Duration::from_secs(notify_at)
} else {
next_notify
}
} else {
let notify_at = -self.data.delivery_by as u64;
if expire_secs > notify_at {
Duration::from_secs(expire_secs - notify_at)
} else {
next_notify
}
};
let mut notify = queue::Schedule::later(future_release + notify);
notify.inner = (num_intervals - 1) as u32; // Disable further notification attempts
(notify, now() + expire_secs)
};
// Update domain
let domain = message.domains.last_mut().unwrap();
domain.retry = retry;
domain.notify = notify;
domain.expires = expires;
}
message.recipients.push(queue::Recipient {
address: rcpt.address,
address_lcase: rcpt.address_lcase,
status: queue::Status::Scheduled,
flags: if rcpt.flags
& (RCPT_NOTIFY_DELAY
| RCPT_NOTIFY_FAILURE
| RCPT_NOTIFY_SUCCESS
| RCPT_NOTIFY_NEVER)
!= 0
{
rcpt.flags
} else {
rcpt.flags | RCPT_NOTIFY_DELAY | RCPT_NOTIFY_FAILURE
},
domain_idx: (message.domains.len() - 1) as u32,
orcpt: rcpt.dsn_info,
});
}
message
}
pub async fn can_send_data(&mut self) -> Result<bool, ()> {
if !self.data.rcpt_to.is_empty() {
if self.data.messages_sent
< self
.server
.eval_if(
&self.server.core.smtp.session.data.max_messages,
self,
self.data.session_id,
)
.await
.unwrap_or(10)
{
Ok(true)
} else {
trc::event!(
Smtp(SmtpEvent::TooManyMessages),
SpanId = self.data.session_id,
Limit = self.data.messages_sent
);
self.write(b"452 4.4.5 Maximum number of messages per session exceeded.\r\n")
.await?;
Ok(false)
}
} else {
trc::event!(
Smtp(SmtpEvent::RcptToMissing),
SpanId = self.data.session_id,
);
self.write(b"503 5.5.1 RCPT is required first.\r\n").await?;
Ok(false)
}
}
fn write_received(&self, headers: &mut Vec<u8>, id: u64) {
headers.extend_from_slice(b"Received: from ");
headers.extend_from_slice(self.data.helo_domain.as_bytes());
headers.extend_from_slice(b" (");
headers.extend_from_slice(
self.data
.iprev
.as_ref()
.and_then(|ir| ir.ptr.as_ref())
.and_then(|ptr| ptr.first().map(|s| s.strip_suffix('.').unwrap_or(s)))
.unwrap_or("unknown")
.as_bytes(),
);
headers.extend_from_slice(b" [");
headers.extend_from_slice(self.data.remote_ip.to_string().as_bytes());
headers.extend_from_slice(b"]");
if self.data.asn_geo_data.asn.is_some() || self.data.asn_geo_data.country.is_some() {
headers.extend_from_slice(b" (");
if let Some(asn) = &self.data.asn_geo_data.asn {
headers.extend_from_slice(b"AS");
headers.extend_from_slice(asn.id.to_string().as_bytes());
if let Some(name) = &asn.name {
headers.extend_from_slice(b" ");
headers.extend_from_slice(name.as_bytes());
}
}
if let Some(country) = &self.data.asn_geo_data.country {
if self.data.asn_geo_data.asn.is_some() {
headers.extend_from_slice(b", ");
}
headers.extend_from_slice(country.as_bytes());
}
headers.extend_from_slice(b")");
}
headers.extend_from_slice(b")\r\n\t");
if self.stream.is_tls() {
let (version, cipher) = self.stream.tls_version_and_cipher();
headers.extend_from_slice(b"(using ");
headers.extend_from_slice(version.as_bytes());
headers.extend_from_slice(b" with cipher ");
headers.extend_from_slice(cipher.as_bytes());
headers.extend_from_slice(b")\r\n\t");
}
headers.extend_from_slice(b"by ");
headers.extend_from_slice(self.hostname.as_bytes());
headers.extend_from_slice(b" (Stalwart SMTP) with ");
headers.extend_from_slice(match (self.stream.is_tls(), !self.is_authenticated()) {
(true, true) => b"ESMTPS",
(true, false) => b"ESMTPSA",
(false, true) => b"ESMTP",
(false, false) => b"ESMTPA",
});
headers.extend_from_slice(b" id ");
headers.extend_from_slice(format!("{id:X}").as_bytes());
headers.extend_from_slice(b";\r\n\t");
headers.extend_from_slice(Date::now().to_rfc822().as_bytes());
headers.extend_from_slice(b"\r\n");
}
}