The mailing list for listmasters using Sympa

[IKEDA Soji <address@concealed>]

Hi Tim,

On 2022/10/12 2:49, Silvers, Tim wrote:
> Thanks everyone for your input. I do believe this is an issue with the 
> emails from O365 just having a lot of extraneous headers, as I found in 
> my investigation and supported by Soji. I’d rather address this locally 
> by just adjusting the header size limit, as we have a lot of lists and 
> subscribers using these platforms that don’t restrict their header size. 
> That is better than telling all of our subscribers that their email 
> provider needs to change something, or that we have to strip headers for 
> them.
>
> The Postfix documentation states in the header_checks man page, “Message 
> headers that are longer than $header_size_limit characters are 
> truncated.” So, why is this even a problem? The default is 102400 and we 
> have not changed it. Yet the error in the logs (e.g., “stat=Headers too 
> large (32768 max)”) is the sendmail limit [2]. So, I am a big confused.

An example error message in Postfix's log is as following:

| host mail.example.fr [xxx.xxx.xxx.xxx] said: 552 5.6.0 Headers too 
large (32768 max) (in reply to end of DATA command)

This error message is not reported by your mailing list server
(Postfix), but by the destination mail server (probably Sendmail).

Your mailing list server is not the cause of this problem.
Some senders (e.g. Office 365) and/or receivers (e.g. Sendmail) are the
cause.


Regards,
-- Soji

> [1] postconf -d | grep header
>
> always_add_missing_headers = no
>
> canonical_classes = envelope_sender, envelope_recipient, header_sender, 
> header_recipient
>
> detect_8bit_encoding_header = yes
>
> header_address_token_limit = 10240
>
> header_checks =
>
> header_size_limit = 102400
>
> …
>
> [2] grep -ri maxheaders /etc/mail/
>
> /etc/mail/sendmail.cf:#O MaxHeadersLength=32768
>
> /etc/mail/submit.cf:#O MaxHeadersLength=32768
>
> Tim
>
> *From: *address@concealed <address@concealed> on 
> behalf of IKEDA Soji <address@concealed>
> *Date: *Monday, October 10, 2022 at 10:48 PM
> *To: *Silvers, Tim <address@concealed>
> *Cc: *en@sympa <address@concealed>
> *Subject: *[External] Re: [en@sympa] Headers too large
>
> This message was sent from a non-IU address. Please exercise caution 
> when clicking links or opening attachments from external sources.
> -------
>
> Hi Tim,
>
> On 2022/10/11 0:51, Silvers, Tim wrote:
>  > Hi. We are running Sympa 6.2.68 on CentOS 7 with Postfix as our MTA. We
>  > had a user report that some emails to their list are not being
>  > distributed. Logs show “headers too large (32768 max)” errors for these
>  > messages. The only reference I see to this limit is in Sendmail [1], but
>  > as I stated, we are using Postfix. I found nothing in the Sympa config
>  > in reference to header size either, just message size.
>  >
>  > Searching this error turns up a lot of references to O365 email headers
>  > being rather long and running into this default header size limit; the
>  > sending site is using O365. The fix seems to be for other MTAs to
>  > increase the header size limit. But how do I do that?
>  >
>  > Has anyone else encountered this problem?
>  >
>  > [1] /etc/mail/sendmail.cf:#O MaxHeadersLength=32768
>  >
>  > /etc/mail/submit.cf:#O MaxHeadersLength=32768
>
> Also on this list en@sympa, there are subscribers that do sometimes not
> receive messages due to this problem.  (However, on this list, the
> problem has occurred only with the site setting MaxHeadersLength to
> 16384 bytes: See also below).
>
> This problem is essentially due to the fact that some senders does not
> care about large header and some receivers have a small header size
> limit.
>
>     - Such senders include Microsoft Office 365 (Exchange Online) and
>       certain versions of Cisco IronPort (Email Security Appliance).
>
>     - Such receivers include Sendmail and Symantec Email Security.cloud.
>
> An essential solution would be for the senders not to add header fields
> that are only useful for their own architecture (*) so that the
> recipients with small size of limit (**) won't reject messages.
>
> (*) On o365, it appears to be some sort of bug that the messages are
>       sent out with some long header fields kept unremoved.  There is an
>       instruction on how to create a transport rules to remove these
>       fields:
>
>         -
> https://nam12.safelinks.protection.outlook.com/?url=https%3A%2F%2Fanswers.microsoft.com%2Fen-us%2Fmsoffice%2Fforum%2Fall%2Fe%2F80a3b4a1-d0da-4808-9f04-0942463ddfb3%23LastReply&amp;data=05%7C01%7Ctsilver%40iu.edu%7C9029bc138e92416a6b1308daab33116b%7C1113be34aed14d00ab4bcdd02510be91%7C0%7C0%7C638010533081292391%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&amp;sdata=UjGFO2vgELI8X%2Bwz5zzHBZgtfRtxQliuO53ZpnDF0bI%3D&amp;reserved=0
>  
> <https://nam12.safelinks.protection.outlook.com/?url=https%3A%2F%2Fanswers.microsoft.com%2Fen-us%2Fmsoffice%2Fforum%2Fall%2Fe%2F80a3b4a1-d0da-4808-9f04-0942463ddfb3%23LastReply&amp;data=05%7C01%7Ctsilver%40iu.edu%7C9029bc138e92416a6b1308daab33116b%7C1113be34aed14d00ab4bcdd02510be91%7C0%7C0%7C638010533081292391%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&amp;sdata=UjGFO2vgELI8X%2Bwz5zzHBZgtfRtxQliuO53ZpnDF0bI%3D&amp;reserved=0>
>
> (**) The header size limits in many mail systems are larger than 32768
>       bytes:
>
>         - 
> https://nam12.safelinks.protection.outlook.com/?url=https%3A%2F%2Fwww.mail-archive.com%2Fmailop%40mailop.org%2Fmsg02856.html&amp;data=05%7C01%7Ctsilver%40iu.edu%7C9029bc138e92416a6b1308daab33116b%7C1113be34aed14d00ab4bcdd02510be91%7C0%7C0%7C638010533081292391%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&amp;sdata=5R6auccy7E43iDQWId8hPkD7FNKzlHDxe2Xp%2FYvyRNg%3D&amp;reserved=0 <https://nam12.safelinks.protection.outlook.com/?url=https%3A%2F%2Fwww.mail-archive.com%2Fmailop%40mailop.org%2Fmsg02856.html&amp;data=05%7C01%7Ctsilver%40iu.edu%7C9029bc138e92416a6b1308daab33116b%7C1113be34aed14d00ab4bcdd02510be91%7C0%7C0%7C638010533081292391%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&amp;sdata=5R6auccy7E43iDQWId8hPkD7FNKzlHDxe2Xp%2FYvyRNg%3D&amp;reserved=0>
>
>       Therefore, administrators of Sendmail are suggested at least not to
>       set a limit smaller than this, i.e. its default.
>
>
> Regards,
> -- Soji
>
>  > Thanks,
>  >
>  > Tim
>  >

--
株式会社 コンバージョン
ITソリューション部 システムソリューション1グループ 池田荘児
e-mail address@concealed
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