https://bugs.exim.org/show_bug.cgi?id=1885
Bug ID: 1885
Summary: Mail heisenbounces. Probable cause: IPv6 and/or lack
of encryption.
Product: Exim
Version: 4.84
Hardware: x86-64
OS: Linux
Status: NEW
Severity: bug
Priority: medium
Component: Transports
Assignee: nigel@???
Reporter: thb@???
CC: exim-dev@???
This bug report's summary line is cryptic because I am unable to summarize it
in one line. However, in not too many lines:
1. I use Exim4 on two machines: a relay host (smarthost) in a data center; and
a DHCP-connected laptop on my desk.
2. Communication between the two machines is secured by a plaintext password
after STARTTLS on port 587.
3. Until I worked around the problem, mail sent from the laptop would
heisenbounce. That is, it would often go through, but would bounce from the
relay host sporadically.
4. Much investigation discovered two likely culprits: [a] IPv6 operations by
the relay host, which has no IPv6 interface; and/or [b] an unnecessary,
unhelpful attempt by the laptop to fall back to unencrypted transmission if
encryption failed.
Note that [a] is on the relay host and [b] is on the laptop.
I have worked around both [a] and [b]. So far, the heisenbouncing seems to
have stopped. I cannot tell you whether it was workaround [a] or workaround
[b] that stopped it. (Indeed, I am not wholly sure that the heisenbouncing has
stopped. That's the thing about heisenbugs, isn't it? Appearing sporadically,
they are hard to duplicate or isolate.) However, either or both of [a] and [b]
might want attention from you in any event, at your discretion.
I reported this bug first to Debian [1], whose Exim4 packages I use. After
reviewing the report, Debian's Exim4 maintainer suggests that I report the bug
here.
[1] https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=837535
A full discussion of the bug, its effects, the various workarounds tried, and
so on, is found here [2]:
[2] http://unix.stackexchange.com/q/308283/18202
The linked discussion has the form of a question and some answers. I suggest
that you consult the question and two of the answers: the answers by Rui F.
Ribeiro and by @thb (me).
--
You are receiving this mail because:
You are on the CC list for the bug.
