SMTP Error code received doesn't match LMTP response

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#800 opened on Oct 7, 2025 0 comments 0 reactions 1 assignee View on GitHub

@foxcpp is already working on this.

Since Jan 10, 2026.

Assessment

This issue has not been assessed yet.

Description

bug

Description of the bug

When using LMTP to offload IMAP delivery to dovecot for instance, the return SMTP error code is not properly propagated

Steps to reproduce

Send a mail to a maddy server that is using LTMP with dovecot as an IMAP backend
Let's say the recipient is exceeding its quota with this email
Maddy receives back a 552 error code from Dovecot
The error code is rewritten to 452 as per: https://github.com/foxcpp/maddy/blob/master/internal/smtpconn/smtpconn.go#L121 (for legacy support of too many RCPT If I got it correctly ?)
The sender mail server receives back a 554 (Internal server error) from maddy

Log files

Here is a log of the different interaction (sender/receiver/dovecot). Both sender and receiver are running a maddy server:

https://hastebin.milkywan.fr/aqupejalus.pl

Configuration file

Simple LMTP taget:

target.lmtp local_mailboxes {
  targets unix:///var/run/dovecot2/lmtp-maddy
}

Called by a simple message pipeline:

msgpipeline local_routing {
  destination $(local_domains) {
    modify {
      replace_rcpt &local_rewrites
    }
    deliver_to &local_mailboxes
  }
  default_destination {
    reject 550 5.1.1 "User doesn't exist"
  }
}

For dovecot:

service lmtp {
  unix_listener lmtp-maddy {
    mode = 0600
    user = maddy
  }
}

Environment information

maddy version: 0.8.1 linux/amd64 go1.24.6

Dominant language: Go
Stars: 6.1k
Forks: 327
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