Sendmail+Cyrus IMAP "Data format error" and bounces

[Andrea Venturoli]

On 2020-03-17 13:31, Sergey wrote:
> On Tuesday 17 March 2020, Andrea Venturoli wrote:
> 
>>  From time to time, I receive some message that are refused
>> and bounce. Do to possible blacklisting, I *really* want to
>> avoid bounces.
>   
> I use Sendmail+Cyrus a very long time and I not remember this
> problem exactly. Cyrus is not receive messages in two cases:
> 1) message contains 8-bit symbols (not encoded to base64 or
>     QP) in header;
> 2) message contains NUL character.
> 
> The first is subject of reject8bit option in imapd.conf. About second look
> to https://groups.google.com/forum/#!topic/comp.mail.sendmail/xW7S5vXDNtY
> 
> May be the first one causes the "Data format error" message.

Thanks for pointing this out!

I've been fighting the "NUL characters" problem on the sendmail side for 
a long time: it seems I won about some 10 months ago, since I don't see 
any more of these errors in the logs after May.

I'm still seeing bounces, but, as you say, the reason is not the same!



So, focusing on 1), I my imapd.conf I have:

# If enabled, lmtpd rejects messages with 8-bit characters in the 
 
 

# headers.  Otherwise, 8-bit characters are changed to `X'.  (A proper 
 
 

# soultion to non-ASCII characters in headers is offered by RFC 2047 
 
 

# and its predecessors.) 
 
 

# 
 
 

#reject8bit: no

Also, 
https://www.cyrusimap.org/imap/reference/manpages/configs/imapd.conf.html#std:cyrusman-imapd.conf(5), 
says "reject8bit: 0" is the default.

 From this I understand my setup should NOT reject 8bit headers (but 
change non-ASCII characters to X).

I'm now setting this explicitly and I'll see what happens.



  bye & Thanks
	av.

P.S.
Assuming I now receive such messages, what about settings munge8bit: 1?
Any drawback or risk?