550 maximum allowed line length is 998 octets, got 1012

Dean Murphy 1 Reputation point

Running Outlook for Office 365 on Windows 10. I am getting this message immediately on a send/receive: Your message did not reach some or all of the intended recipients. Subject: RE: Craighouse PR Sent: 09/03/2021 14:23 The following recipient(s) cannot be reached: '[name withheld for privacy]' on 09/03/2021 14:23 550 maximum allowed line length is 998 octets, got 1012 Email format options as image ![75923-image.png][1] It's happened on a couple of emails to different people and even happens when I try to send a very short message. Any ideas why this is happening? [1]: /api/attachments/75923-image.png?platform=QnA

Outlook Management
Outlook Management
Outlook: A family of Microsoft email and calendar products.Management: The act or process of organizing, handling, directing or controlling something.
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  1. fundamental4 6 Reputation points

    This is a looooong term problem, so, as I think that microsoft has good programmers, MICROSOFT DOES NOT WANT TO SOLVE THIS PROBLEM.

    As @Nomad is saying, this error appears when "Usually when replying to a long email chain."

    For me the error is in the "Subject" field + some specific email accounts.

    Related to the error: if you forward this long email chain but deleting the whole body of the email, the error is still there.

    What I do: (because I want to keep the whole conversation and the same subject):

    • open a new email.
    • copy/paste the whole conversation in the new email.
    • copy/paste the subject.

    it works for me.

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  2. Rich Watts 6 Reputation points

    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.

    1 person found this answer helpful.
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  3. Jade Liang-MSFT 9,856 Reputation points Microsoft Employee

    Hi @Dean Murphy ,

    Welcome to our forum.

    In order to further confirm your issue, could you send/receive message normally on your web mail? If you also receive the error message there, the issue may be related to your account itself, and it's suggested to contact your admin to get more help.

    If the issue only occurred on your Outlook desktop client, what's the version of your client(File>Office account>About Outlook), please first ensure that you have updated to the latest version of Outlook.

    Based on my research, the line limit usually occurred on plain text or RTF fromat, so what's the format of your emails(HTML, plain text or RTF)? Did the issue have any differences if you switch to other formats before sending the message? Also, the option that you posted in picture may apply to the received message, so I'm afraid it couldn't affect the message you sent.

    Did your recipients all work with Outlook client? In order to further analyze your issue, it's suggested to create a short message(such as with "test" word only) via New Message option and send it to yourself for testing. If you could send to yourself normally, the issue may also be related to the recipients' client.

    If you also couldn't send it to yourself, in order to avoid the interference of add-ins, it's suggested to restart your Outlook in safe mode to check if the issue still exists(Windows + R>type "outlook.exe /safe">enter).

    Hope that would be helpful to you.

    If the response is helpful, please click "Accept Answer" and upvote it.
    Note: Please follow the steps in our documentation to enable e-mail notifications if you want to receive the related email notification for this thread.

  4. Dean Murphy 1 Reputation point

    I know I went quiet for a while but this issue hasn't been resolved and it keeps happening

  5. Kenny Tilley 1 Reputation point

    i have this problem (but only on my office email account) and what i have found is that if any part of the message contained an RTF file/image embedded in the trail, then this gets attached as a separate file and parsed by the outgoing mail server. Inevitably, it doesn't contain any newline characters and thus is treated as a single long line (it always seems to be 1012 "octets"?). The only solutions i have found is to resend the message via gmail, which inevitably works, or as suggested above, swipe the entire message and copy it into a new message (that seems to tidy it up 9 times out of 10).


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