Bug#948271: exim4-daemon-heavy: smtp_ratelimit_rcpt breaks connection instead of just delaying RCPT verbs

[Andreas Metzler]

On 2020-01-06 "Ralf G. R. Bergs" <Ralf+Debian at Bergs.biz> wrote:
[...]
> I have the following config snippet active to hamper spammers
> brute-force trying local-parts on my server:

> ----------- 8x -------------
> smtp_ratelimit_hosts = *
> smtp_ratelimit_rcpt = 4,0.25s,1.2,4m
> ----------- 8x -------------

> I tried to send a message from Thunderbird to 10 recipients, but
> instead of accepting the message an SMTP-level error occurred. Same
> happened with macOS Mail client.

> Apparently the implementation of Exim is faulty, because instead of
> just delaying RCPT verbs it seems to close the connection.

[...]
> After the 5th occurence of an RCPT verb (for address
> "ralf+6 at example.org" in this case) the server seems to close the
> connection:

> ----------- 8x -------------
>      33 0.338365       2a00:6020:1eea:3420:0123:4567:89ab:cdef
> 2a01:4f8:fff:fff::2   SMTP     131    C: RCPT TO:<ralf+6 at example.org>
>      34 0.397162       2a01:4f8:fff:fff::2
> 2a00:6020:1eea:3420:0123:4567:89ab:cdef TCP      74     587 → 63730
> [ACK] Seq=4151 Ack=1287 Win=29952 Len=0
>      35 0.602293       2a01:4f8:fff:fff::2
> 2a00:6020:1eea:3420:0123:4567:89ab:cdef SMTP     117    S: 250 Accepted
>      36 0.603927       2a00:6020:1eea:3420:0123:4567:89ab:cdef
> 2a01:4f8:fff:fff::2   SMTP     131    C: RCPT TO:<ralf+5 at example.org>
>      37 0.617940       2a01:4f8:fff:fff::2
> 2a00:6020:1eea:3420:0123:4567:89ab:cdef SMTP     138    S: 421
> example.net lost input connection
> ----------- 8x -------------

> When I removed the above config snippet I could properly send the
> message with more than 5 recipients.

> Unfortunately at the moment I have no means of trying a more recent
> version of Exim -- I can only update to the latest oldstable version.

> Many thanks in advance for looking into this.
[...]

Hello,

I cannot reproduce this with 4.93, it just works as expected.

cu Andreas