> On 24 March 2019 12:43 Daniel Lange <dla...@debian.org> wrote: > > > Hi Aki, > > Am 21.02.19 um 12:55 schrieb Aki Tuomi: > > > > On 21.2.2019 13.47, Lionel Elie Mamane via dovecot wrote: > >> I noticed a mail stuck in my mail queue. dovecot-lda was returning > >> error 64 Invalid parameter given. (EX_USAGE). > >> > >> Weird, weird, weird. After some sleuthing, I found the sender address > >> was firstl...@domain.tld, with a UTF8-encoded Unicode U+FEFF ZERO > >> WIDTH NO-BREAK SPACE character (AKA byte order mark) between "First" > >> and "Last" :) > >> > >> Since that is passed as the -f parameter to dovecot-lda, it was giving > >> the 64 error. > > > > Your MTA should not be passing this along. > > Unfortunately Postfix does. > It honors the robustness principle (~Postel's law) and therefore > accepts envelope senders like > > from=<<U+FEFF>jamesbr...@triolan.net> > or > from=<Gerald<U+FEFF>sm...@nampaichuanlondon.com> > or > from=<Peter???sm...@taotalk.nl> > (invalid 3-byte UTF-8 .) > > which are increasingly making rounds. > > With a working local delivery these will just feed spamassassin or > rspamd and all is well. And may be the occasional poor Exchange > customer's email is delivered, too. > > With Dovecot 2.3.4.1 and 2.3.5 dovecot-lda and lmtp > these will generate bounces that lead to backscatter spam: > > postfix/pipe[22438]: D8C5E35C2600: to=<redacted@redacted>, relay=dovecot, > delay=0.22, delays=0.14/0.01/0/0.08, dsn=5.3.0, status=bounced (command line > usage error. Command output: lda: Fatal: Invalid -f parameter: Invalid > character in localpart ) > postfix/cleanup[22433]: 0D95435C25EF: message-id=<redacted> > postfix/bounce[22440]: D8C5E35C2600: sender non-delivery notification: > 0D95435C25EF > (dovecot-lda case) > > and > > postfix/lmtp[12829]: 6ADF135C2671: to=<redacted>, > relay=redacted[private/dovecot-lmtp], delay=0.17, delays=0.15/0.01/0.01/0, > dsn=5.5.2, status=bounced (host redacted[private/dovecot-lmtp] said: 500 > 5.5.2 Invalid command syntax (in reply to MAIL FROM command)) > ... > (lmtp case) > > In my book an LDA should do its job and deliver the email. It should > complain about an invalid envelope sender if (and only if) it needs to > send a bounce (and thus will send that to MAILER-DAEMON instead). But it > must in no case refuse to deliver the email to a perfectly valid local > recipient. Yes, the envelope sender is flawed. But that is not the LDAs > concern. If the SMTPD was happy enough, the email has been accepted and > must not lead to a late bounce. In the case we're currently seeing this > leads to backscatter spam. > > I think the right logic would be to not smtp_address_parse_path the > enveloper sender unless it is needed for legitimate bounces (e.g. > mailbox over quota). In that case a failing enveloper sender should be > replaced for the bounce. In any other case dovecot-lda and lmtp must not > bother. > > Kind regards, > Daniel
We are tracking this as DOP-1045. Aki
