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add option to ruleset to accept incoming spammy messages to a configured mailbox

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this is based on @bobobo1618's PR #50. bobobo1618 had the right idea, i tried
including an "is forwarded email" configuration option but that indeed became
too tightly coupled. the "is forwarded" option is still planned, but it is
separate from the "accept rejects to mailbox" config option, because one could
still want to push back on forwarded spam messages.

we do an actual accept, delivering to a configured mailbox, instead of storing
to the rejects mailbox where messages can automatically be removed from.  one
of the goals of mox is not pretend to accept email while actually junking it.
users can still configure delivery to a junk folder (as was already possible),
but aren't deleted automatically. there is still an X-Mox-Reason header in the
message, and a log line about accepting the reject, but otherwise it is
registered and treated as an (smtp) accept.

the ruleset mailbox is still required to keep that explicit. users can specify
Inbox again.

hope this is good enough for PR #50, otherwise we'll change it.
This commit is contained in:
Mechiel Lukkien
2023-08-09 18:03:29 +02:00
parent 383fe4f53a
commit 9c31789c56
9 changed files with 98 additions and 35 deletions
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44
smtpserver/analyze.go
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@ -38,6 +38,7 @@ type delivery struct {
type analysis struct {
accept bool
mailbox string
code int
secode string
userError bool
@ -67,27 +68,43 @@ const (
)
func analyze(ctx context.Context, log *mlog.Log, resolver dns.Resolver, d delivery) analysis {
reject := func(code int, secode string, errmsg string, err error, reason string) analysis {
return analysis{false, code, secode, err == nil, errmsg, err, nil, nil, reason}
mailbox := d.rcptAcc.destination.Mailbox
if mailbox == "" {
mailbox = "Inbox"
}
// If destination mailbox has a mailing list domain (for SPF/DKIM) configured,
// check it for a pass.
// todo: should use this evaluation for final delivery as well
rs := store.MessageRuleset(log, d.rcptAcc.destination, d.m, d.m.MsgPrefix, d.dataFile)
if rs != nil {
mailbox = rs.Mailbox
}
if rs != nil && !rs.ListAllowDNSDomain.IsZero() {
ld := rs.ListAllowDNSDomain
// todo: on temporary failures, reject temporarily?
if d.m.MailFromValidated && ld.Name() == d.m.MailFromDomain {
return analysis{accept: true, reason: reasonListAllow}
return analysis{accept: true, mailbox: mailbox, reason: reasonListAllow}
}
for _, r := range d.dkimResults {
if r.Status == dkim.StatusPass && r.Sig.Domain == ld {
return analysis{accept: true, reason: reasonListAllow}
return analysis{accept: true, mailbox: mailbox, reason: reasonListAllow}
}
}
}
reject := func(code int, secode string, errmsg string, err error, reason string) analysis {
accept := false
if rs != nil && rs.AcceptRejectsToMailbox != "" {
accept = true
mailbox = rs.AcceptRejectsToMailbox
d.m.IsReject = true
// Don't draw attention, but don't go so far as to mark as junk.
d.m.Seen = true
log.Info("accepting reject to configured mailbox due to ruleset")
}
return analysis{accept, mailbox, code, secode, err == nil, errmsg, err, nil, nil, reason}
}
if d.dmarcUse && d.dmarcResult.Reject {
return reject(smtp.C550MailboxUnavail, smtp.SePol7MultiAuthFails26, "rejecting per dmarc policy", nil, reasonDMARCPolicy)
}
@ -166,20 +183,13 @@ func analyze(ctx context.Context, log *mlog.Log, resolver dns.Resolver, d delive
// per-mailbox. If referenced mailbox is not found (e.g. does not yet exist), we
// can still determine a reputation because we also base it on outgoing
// messages and those are account-global.
mailbox := d.rcptAcc.destination.Mailbox
if mailbox == "" {
mailbox = "Inbox"
}
if rs != nil {
mailbox = rs.Mailbox
}
mb, err := d.acc.MailboxFind(tx, mailbox)
if err != nil {
return fmt.Errorf("finding destination mailbox: %w", err)
}
if mb != nil {
// We want to deliver to mb.ID, but this message may be rejected and sent to the
// Rejects mailbox instead, which MailboxID overwritten. Record the ID in
// Rejects mailbox instead, with MailboxID overwritten. Record the ID in
// MailboxDestinedID too. If the message is later moved out of the Rejects mailbox,
// we'll adjust the MailboxOrigID so it gets taken into account during reputation
// calculating in future deliveries. If we end up delivering to the intended
@ -203,12 +213,12 @@ func analyze(ctx context.Context, log *mlog.Log, resolver dns.Resolver, d delive
log.Info("reputation analyzed", mlog.Field("conclusive", conclusive), mlog.Field("isjunk", isjunk), mlog.Field("method", string(method)))
if conclusive {
if !*isjunk {
return analysis{accept: true, dmarcReport: dmarcReport, tlsReport: tlsReport, reason: reason}
return analysis{accept: true, mailbox: mailbox, dmarcReport: dmarcReport, tlsReport: tlsReport, reason: reason}
}
return reject(smtp.C451LocalErr, smtp.SeSys3Other0, "error processing", err, string(method))
} else if dmarcReport != nil || tlsReport != nil {
log.Info("accepting dmarc reporting or tlsrpt message without reputation")
return analysis{accept: true, dmarcReport: dmarcReport, tlsReport: tlsReport, reason: reasonReporting}
return analysis{accept: true, mailbox: mailbox, dmarcReport: dmarcReport, tlsReport: tlsReport, reason: reasonReporting}
}
// If there was no previous message from sender or its domain, and we have an SPF
// (soft)fail, reject the message.
@ -244,7 +254,7 @@ func analyze(ctx context.Context, log *mlog.Log, resolver dns.Resolver, d delive
pass := err == nil
log.Infox("pass by subject token", err, mlog.Field("pass", pass))
if pass {
return analysis{accept: true, reason: reasonSubjectpass}
return analysis{accept: true, mailbox: mailbox, reason: reasonSubjectpass}
}
}
@ -324,7 +334,7 @@ func analyze(ctx context.Context, log *mlog.Log, resolver dns.Resolver, d delive
}
if accept {
return analysis{accept: true, reason: reasonNoBadSignals}
return analysis{accept: true, mailbox: mailbox, reason: reasonNoBadSignals}
}
if subjectpassKey != "" && d.dmarcResult.Status == dmarc.StatusPass && method == methodNone && (dnsblocklisted || junkSubjectpass) {