How to stop message headers growing too long in Outlook?

Robert 0

We're having problems where we're getting "message has lines too long for transport" errors. We've been in contact with our email provider and they have said the issue is the message headers coming from Outlook are too long.

Part of their reply to our support request:

Every time you reply on a thread, Outlook generates a reference ID and adds it to the email header making it extremely large and eventually causing an error "message has lines too long for transport".

The only solutions they could propose was don't use Outlook, or start a new email chain regularly. If its only Outlook causing this issue, surely its a bug that could be fixed, or a setting that could be changed?

To pre-emptively answer some questions posed by the AI response:

We're using HTML message format, not rich text
This apply to emails both with and without attachments.
This is the desktop version of Outlook that come with Microsoft Office Home and Business 2019

ChristyZhang-MSFT 22,951 Reputation points Microsoft Vendor

2024-02-05T02:40:13.19+00:00

Hi @Robert ,

Welcome to our forum!

We're having problems where we're getting "message has lines too long for transport" errors.

When do you encounter the issue?

Does this issue occur with all emails or some specific emails?

And do other users around you encounter the same issue?

The only solutions they could propose was don't use Outlook, or start a new email chain regularly. If its only Outlook causing this issue, surely its a bug that could be fixed, or a setting that could be changed?

In order to further confirm the issue is related to Outlook desktop client, it's suggested that you could try to add your account to other email client(Mail) to check if the issue persists.
Robert 0 Reputation points

2024-02-05T09:37:10.7666667+00:00

In the latest case, it happened after 19 back and forth emails between a group of approx. 5-6 email accounts; some internal, some external. I just checked the the "References:" bit in that failed email's headers and it was 1013 characters long. The issue affects all accounts on our domain, we all use outlook as our primary mail app. Next time it happens, I'll check how our webmail portal handles it.
ChristyZhang-MSFT 22,951 Reputation points Microsoft Vendor

2024-02-07T09:03:53.67+00:00

Hi @Robert , Thanks for your reply!

What about your webmail portal?
ChristyZhang-MSFT 22,951 Reputation points Microsoft Vendor

2024-02-15T01:29:20.66+00:00

Hi @Robert ,

I am writing to see how everything is going on with this thread. Should you need more help on this, you can feel free to post back.
Robert 0 Reputation points

2024-02-15T09:00:24.4266667+00:00

@ChristyZhang-MSFT the problem happens rarely. Maybe 2-3 times a year. Next time it happens I will try your suggestion of using the webmail portal and report back. Thank you.
ChristyZhang-MSFT 22,951 Reputation points Microsoft Vendor

2024-02-16T08:37:19.7933333+00:00

Hi @Robert ,

Thanks for your reply! Hope you don't get bothered by this problem anymore. Have a nice day!
Robert 0 Reputation points

2024-02-21T09:26:03.2466667+00:00

@ChristyZhang-MSFT I've just had the error again. This time I tried to re-send via webmail and there was no issue. So I'm confident the issue is with Microsoft Outlook. When I replied to my customer's email via outlook, the "References: " line in the headers was 1013 characters long and caused a delivery failure. When I replied via our webmail portal, the "References: " line was wrapped so there was only one reference per line, meaning the max line length was only around 100 characters. I'm led to believe its Outlook that uses and inserts these references, so why is it the only one that doesn't wrap them? Any help fixing the issue would be appreciated.
ChristyZhang-MSFT 22,951 Reputation points Microsoft Vendor

2024-03-05T09:01:05.3766667+00:00
Hi @Robert ,

Thanks for your reply!

Please try to open Outlook and go to the File menu to check if there're any differences:

Select Options.

Within Outlook Options, choose Mail.

Scroll down to Message format.

In the Automatically wrap text at character field, enter a number between 65 and 70. This indicates where you want Outlook to wrap text.

Select OK to apply the changes and close the window.
Robert 0 Reputation points

2024-03-05T10:09:54.07+00:00

Hi @ChristyZhang-MSFT

Thanks for all the suggestions, I really appreciate you trying to fix this issue.

I checked the setting and it was already set to 76, so I don't think this will stop the 1000 character header lines, but I have now changed it to 70.

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How to stop message headers growing too long in Outlook?

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