550 maximum allowed line length is 998 octets, got 1012

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RichWatts

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Outlook 365 64 bit
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When an email is replied to in Windows Outlook, an item is added to the "References" header. This header keeps growing in size on each reply until it is split up by Outlook at 1012 characters. The problem is that the RFC SMTP line length limit is 998 characters, resulting in many servers rejecting the message as having lines that are too long.

This issue has persisted for many years and Microsoft seems uninterested in fixing it. All it requires is for them to reduce the references header split length in Windows Outlook to 998 characters.

Will Microsoft ever fix this?
 
Honestly, if its been a problem for years... no, it won't be fixed.

There is a new problem with BDAT - error message something like this-
>>
This is not possible through the DATA command of the SMTP protocol, and the receiving system does not support BDAT.
<<

The following article from Microsoft explains it - which doesn't help much because the receiving server needs to fix it or because you have to use a different email client. Fix email delivery issues for error code 550 5.6.11 in Exchange Online
 
Deducting 12 characters from the header, i.e. "references: ", gets us very close to the 998 character limit, almost as if the developers forgot to consider these characters in the limit.

It's just so baffling they knew they needed to split the line to avoid tripping SMTP RFC limits, but implemented the wrong character limit. Bah!
 
Deducting 12 characters from the header, i.e. "references: ", gets us very close to the 998 character limit, almost as if the developers forgot to consider these characters in the limit.
... or they didn't think anyone would hit the limit...
 
... or they didn't think anyone would hit the limit...

It's relatively rare, but some contacts keep replying to the same email chain instead of starting fresh ones, which keeps incrementing the references header until it is at 1012 characters. The tedious workaround is to copy/paste the old email content into a brand new email instead of hitting reply.
 
So you have some of them too? Even though I tell them its easier to start a new message and start typing in the recipients name, they still do it their (slower) way. But it's better than one client who starts a new thread for everything....

The proper thing to do when the subject changes is to start a new thread... and no references. I thought Outlook did that, but it probably won't remove the references if the sender is using a client that doesn't remove the headers.
 
Yes, I think the references header will grow as long as "reply" is used and not "new". All other email clients seem to limit the size of this header, including the Mail app bundled with Windows.

I'm trying to find out a way to automatically split this header on receipt in Exim, although changing 1012 to 998 in in the Outlook source code would be much better!
 
I found an active thread complaining about this issue: Redirecting

I've posted the "New Email" workaround at the end which will hopefully help some people.
 
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