Re: Sendmail+Cyrus IMAP "Data format error" and bounces

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On 2020-03-17 23:49, Andrea Venturoli wrote:
_ sendmail is SMTPUTF8-aware (this is confirmed by EHLO); however Cyrus isn't?

Could be.  This option in imapd.conf might be relevant:

rfc2047_utf8: 0

If enabled, imapd will parse any non-encoded character sequence in MIME header values as UTF8. This is useful for installations that either advertise the UTF8SMTP (RFC 5335) extension or receive mails with improperly escaped UTF-8 byte sequences. It is recommended that this option is left disabled unless there is good reason to do otherwise.

[source: https://www.cyrusimap.org/imap/reference/manpages/configs/imapd.conf.html]

_ 5.6.7 means either the sender or the recipient is not ASCII:
  however I can see for sure that, at least in certain cases, the recipient is in fact ASCII (all my addresses are);   possibly the sender isn't: altough in the logs I see an ASCII address, it might not be and it gets *represented* in ASCII? I'd find this strange, though;

_ or, possibly, other headers are non ASCII: that's what I thought prior to your mail and it still seems more probable to me, but then I should see 5.6.9 (or 5.6.8?), not 5.6.7.

I wondered about that too.  I couldn't tell, and probably you can't either unless you can see all the headers in the messages that are being rejected.  I'd see this as an opportunity: now you can probably craft your own SMTP conversation to deliberately trigger the 5.6.7 rejection, and not have to wait for fate to deliver one to your server.

It may also be instructive to temporarily disable UTF8SMTP in sendmail and see if that changes the rejection behaviour.  Do this carefully because you may reject more that you intended.

In any case, I'm fine if these messages are plainly rejected; I'm not fine if they are accepted and then bounced. I guess this means the problem lies between sendmail and Cyrus, with the former accepting it and, only afterwards, the latter refusing it.
Any way to configure one of the two to avoid this?

The config for that would be on the sendmail side, so I don't know.  Perhaps there's a way for sendmail to keep the connection from the sender open until it has attempted delivery to Cyrus; then sendmail could reject the sender's initial SMTP connection without having to generate a bounce message. Once you are armed with proof that Cyrus is rejecting these messages, you could take that back to the sendmail group and see if they can help.

--
Deborah Pickett
System Administrator
Polyfoam Australia Pty Ltd

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