Outlook 2016 renders horizontal lines seemingly randomly in HTML emails RRS feed

  • Question

  • Hello,

    I tried to get an answer to how to contact an Outlook dev from a "Microsoft Answer Tech". Obviously didn't, don't know why I wasted an hour with that.

    So I'll just try my luck here.

    Outlook 2016 renders strange horizontal lines in HTML emails after tables. No other Outlook does this. Or any other email client.

    The lines are the color of the background. So, if a background-color is defined for html or body, the lines are that color. Otherwise they are white. They are not entirely random, as sending the same HTML email several times yields the same result every time. But they are hard to predict. Adding table rows, changing font-size and line-height seem to change their places.

    Here are several email newsletter campaign communities baffled by the issue:

    • https://litmus.com/community/discussions/5286-mysterous-white-line-in-outlook
    • https://mosaico.io/email-client-tricks/outlook-2016-weird-1px-horizontal-lines/
    • https://www.emailonacid.com/forum/viewthread/786
    • https://github.com/voidlabs/mosaico/issues/93
    Wednesday, June 15, 2016 3:37 PM

All replies

  • Hi,

    Since Outlook 2007, Outlook changed the html rendering engine from Internet Explorer to Microsoft Word based engine for some reasons. This results in limited HTML and CSS support limitations. Currently, the only method is to open HTML emails in web browser via Actions-> View in Browser.

    Here is an article descripted the HTML rendering issue of Outlook in details, you may want to have a look at it:


    Please Note: Since the web site is not hosted by Microsoft, the link may change without notice. Microsoft does not guarantee the accuracy of this information.

    Thank you for your understanding and support.


    Steve Fan
    TechNet Community Support

    Please mark the reply as an answer if you find it is helpful.

    If you have feedback for TechNet Support, contact tnmff@microsoft.com.
    Thursday, June 16, 2016 6:49 AM
  • This is a Outlook 2016 specific bug. It does not appear in Outlook 2007, 2010 or 2013, all of which are using the Word engine. It also does not appear in Outlook 2011 or 2016 iOS version, which for whatever reasons don't use the Word engine.

    So there is no way for an Outlook developer to take a look at this?

    EDIT: HTML rendering capability has deteriorated with each new version. Are you going to blame an obvious bug like this on the Word engine, and do nothing about it? What are we supposed to tell our clients? "Sorry, purchasing Outlook 2016 was a mistake. Try to get your hands on Outlook 2000, as the 16 year old piece of software has better rendering capability than a brand new one."

    That is not a hyperbole. Out of all Outlooks, 2000 is by far the best at rendering HTML.

    I'll spell it as clear as I can: Outlook 2016 is rendering a horizontal line at the end of a <table>. The line is the color of the background. It is not entirely random, but it is difficult to predict, and it has something to do with font-sizes and line-heights. The same bug will probably appear in Word too, when using tables.

    • Edited by NurmiSimo Thursday, June 16, 2016 12:06 PM
    Thursday, June 16, 2016 7:23 AM
  • Thanks for the customer service Microsoft, I appreciate it.
    Friday, June 17, 2016 7:38 AM
  • Sorry for the delay. It's a little busy today, and we are researching on this issue. Would you please forward a problematic HTML email to us so that we can check if we have the same issue in our Outlook 2016? If possible, you can send the email to us via GBSD TN Office Information Collection ibsofc@microsoft.com. Please involve the thread URL in the message for easy follow-up.

    Thank you for your patience and understanding.

    Steve Fan
    TechNet Community Support

    Please mark the reply as an answer if you find it is helpful.

    If you have feedback for TechNet Support, contact tnmff@microsoft.com.
    • Marked as answer by NurmiSimo Friday, June 17, 2016 12:32 PM
    • Unmarked as answer by NurmiSimo Friday, June 17, 2016 1:32 PM
    Friday, June 17, 2016 7:46 AM
  • Thank you for the reply. I've sent an HTML email that should contain two unwanted horizontal lines.

    Sorry for my manners, but it is extremely frustrating to get the call center treatment when I'm trying to come forward with an issue that I'm confident is on the Microsoft end.

    It would be greatly appreciated if the issue could be fixed, or at least if there is a way to code around it.

    Thank you.

    Friday, June 17, 2016 12:32 PM
  • Thank you for the reply. I've received the email you forwarded. Do you mean this horizontal lines? It looks like a <hr /> tag in the HTML codes.

    When I viewed the email message in browser, it didn't show the lines, which means this is a HTML rendering issue in Outlook. You may try the following two options and then check if this issue will happen again:

    1. Try unchecking the option "Reduce message size by removing format information not necessary to display the message" in File -> Options -> Mail -> Message format.

    2. Try unchecking the option "Use Cascading Style Sheets (CSS) for appearance of messages" under File -> Options -> Mail -> Message format.

    This won't fix existing emails but it seems to work for future emails.


    Steve Fan
    TechNet Community Support

    Please mark the reply as an answer if you find it is helpful.

    If you have feedback for TechNet Support, contact tnmff@microsoft.com.
    • Proposed as answer by Steve Fan Thursday, June 23, 2016 9:40 AM
    • Marked as answer by Steve Fan Friday, June 24, 2016 9:21 AM
    • Unmarked as answer by NurmiSimo Friday, July 1, 2016 12:49 PM
    • Unproposed as answer by Steve Fan Thursday, July 7, 2016 1:14 AM
    Tuesday, June 21, 2016 1:49 AM
  • Unchecking both or either of the checkboxes did not work for me. Sending the email again after changing settings did not help. Using text zoom with ctrl + mousewheel makes the lines change places.

    Even if changing the settings would do something, the great majority of Outlook users are rolling with default settings. You need to do better than this. Having this lax attitude towards your own product is simply astonishing.

    Unmarked as answer, as it wasn't one.

    Is it too much to ask to have a developer look at this issue?

    EDIT: Any chance you could have a public, official statement about this bug and the lack of will to fix it?
    • Edited by NurmiSimo Monday, July 4, 2016 10:03 AM
    Friday, July 1, 2016 12:53 PM
  • Will you still reply to this chain, or should I start a new one?
    Wednesday, July 6, 2016 11:50 AM
  • Sorry for the inconvenience caused. As this forum is for general questions and feedback related to Microsoft Office, we have no resource to involve a developer. If you want further assistance from a developer, I'd recommend you post a new question to the Outlook for Developers forum:


    Or you can open a phone ticket with Microsoft to get further assistance.

    We'll keep researching on this issue and will inform you if we get any progress.

    Thank you for your understanding and support.


    Steve Fan
    TechNet Community Support

    Please mark the reply as an answer if you find it is helpful.

    If you have feedback for TechNet Support, contact tnmff@microsoft.com.
    • Edited by Steve Fan Thursday, July 7, 2016 1:22 AM
    Thursday, July 7, 2016 1:22 AM
  • Here's what I originally posted on some other Microsoft forum. There are so many of these and I can't seem to find the correct one by either website navigation or Google.


    As seen in the screenshot posted by a Microsoft representative, black lines, or the lines with the color of the body background, appear when they are not supposed to. They seem to appear after tables. Whether they appear or not seems to be affected by font-size and line-height. By changing the order of the tables the lines also appear in different places. Zooming in with the mousewheel also changes where the lines appear. Unchecking the options suggested by the Microsoft representative did not solve the issue.

    It would be greatly appreciated if a solution was found to this problem. Either a patch to Outlook, or a way to code around the issue. People on different HTML email campaign communities have tried tackling this issue, without a result.

    If there is indeed a problem on the Microsoft end, and there will be no effort put into fixing it, please release an official statement regarding this matter. It's not that we have an issue reading emails, we don't use Outlook 2016 for that, but our clients use our service to send emails to their customers, and some of them have made the decision to invest 135€ on a product that does not render HTML emails properly.

    Thank you

    Thursday, July 7, 2016 9:25 AM
  • Hi NurmiSimo,

    I was informed that the Outlook for Developers forum is only for questions and feedback related to Outlook development that is related to Outlook usage, it's not related to the Outlook product. Sorry for redirecting you to the incorrect forum. I'd recommend you contact Microsoft via Customer Service as there is no direct resource to involve the Outlook product team in the forum. You may also consider to submit a feedback regarding this issue to Microsoft via File > Feedback > Outlook 2016 Feedback in Outlook 2016.


    Steve Fan
    TechNet Community Support

    Please mark the reply as an answer if you find it is helpful.

    If you have feedback for TechNet Support, contact tnmff@microsoft.com.
    Friday, July 8, 2016 2:22 AM
  • Unbelievable. I just told you of a bug in your software, and instead of forwarding it to the correct person/people, you push me to different forums, customers services, whatever.

    I'm going to need your supervisor's email address, thank you.

    Friday, July 8, 2016 7:43 AM
  • Hi NurmiSimo,

    You definitely should not be pushed to other forums. I have gone through this thread, and can fully understand your frustration. As my check, this is actually a known issue, and still under investigation in production group. Sorry I cannot provide a timeframe about when the issue can be fixed now. We will continue tracking the issue and update the status here once it is fixed.

    Thanks for your understanding. Hope the experience in this thread didn't make you lose trust for TechNet. We sincerely welcome you back and discuss any Microsoft product related questions here.

    Best Regards,
    Reken Liu

    TechNet Community Support
    Please remember to mark the replies as answers if they help, and unmark the answers if they provide no help. If you have feedback for TechNet Support, contact tnmff@microsoft.com.

    • Proposed as answer by JPFillion Friday, April 28, 2017 1:44 PM
    • Unproposed as answer by JPFillion Friday, April 28, 2017 1:44 PM
    Monday, July 11, 2016 5:51 AM
  • Any update on this?
    Wednesday, September 14, 2016 10:13 AM
  • We experience same problem in Outlook 2016. Same bug also in Windows 10 Mail. 

    Any update on bug fix?

    Monday, November 7, 2016 12:32 PM
  • Trickling back to revive this thread. Any update on this? 
    Wednesday, March 29, 2017 7:58 PM
  • [...]We will continue tracking the issue and update the status here once it is fixed.

    [...] Hope the experience in this thread didn't make you lose trust for TechNet. [...]

    Best Regards,
    Reken Liu

    Thanks so much for promising to update this thread, you have restored my trust in TechNet. Looking forward to a timely update.
    Friday, April 28, 2017 1:43 PM
  • Any updates on this? 
    Friday, June 2, 2017 9:04 AM
  • Any update on this?
    Friday, June 2, 2017 2:30 PM
  • Any update on this?
    Tuesday, June 20, 2017 9:22 AM
  • Any Update on this?

    I am seeing in Outlook 2016 MSO (16.0.4549.1000)

    tried to post an image, but received message that my account needs to be verified.
    • Edited by K4ren Monday, July 3, 2017 7:36 PM
    Monday, July 3, 2017 7:29 PM
  • Any update on this? Any workaround ?  Except changing app for opening emails?
    It happens to me , on different resolutions and on different scale, sometimes appears at bottom of the invisible table, sometimes at right  border of the table, there is no rule or logic, it just appears and disappears when zooming in/out.
    • Edited by NevenaLena Tuesday, July 25, 2017 6:46 AM
    Tuesday, July 25, 2017 6:39 AM
  • I get a similar problem on some of my html pages if I view them in the Microsoft Edge browser. There are random horizontal lines that appear and match any border color I may have. If I hit Refresh, they may disappear or they may appear in different places. They do not appear in FireFox or Chrome. They are NOT caused by <hr> tags.
    Tuesday, January 2, 2018 7:30 PM
  • I think I may have figured out a fix for this problem. I simply removed the background colour from the <body> and applied it to a <table> that houses all of the code. Give it a try it worked for me.  
    Tuesday, January 23, 2018 5:33 AM
  • Hi Reken Liu

    Is there any fixes, a workaround or just any news about the issue? Our company has migrated to o365 lately (over 30K workplaces) and we experience the same issue as described in this thread.

    Best regards


    Tuesday, June 19, 2018 9:13 AM
  • Bump/Any updates? 

    So far aside from some only occasionally effective advice regarding changing line heights and font sizes to even numbers and setting exact td heights which doesn't work in responsive emails and doesn't work consistently there doesn't seem to be a fix for this. 

    Last promise for 'investigation and updates' made on the 28th of April.... nothing since sounds like it isn't being investigated very hard. 

    Thursday, August 2, 2018 3:44 PM
  • I found a Workaround for me.

    Before i had this to make 20px space between to blocks

        <td>Some Content</td>
        <td style="line-height:0; font-size:0; height:20px">&nbsp;</td>
        <td>Some Content</td>

    When i change it to this code the white lines are gone:

        <td>Some Content</td>
        <td style="line-height:0; font-size:0; height:20px">
        <td>Some Content</td>

    Additionally i had some white lines left around images.
    When i make the images ist actual height plus 1px those lines are gone aswell.
    (So on a image thats 300px height i added height="301")
    It might also work to change the ratio of the image, but i didn't try that.

    Hope that helps someone.

    Wednesday, August 8, 2018 9:08 AM
  • So any update so far? I see the issue is still happening to Outlook 2016 and Outlook 365
    Wednesday, June 5, 2019 3:55 PM
  • Hi, is there an update? This bug now is not only showing up in Outlook 2016 but also in newer Outlook versions and even in Windows Mail on Windows 10.

    Thursday, August 8, 2019 3:03 PM
  • 16. August 2019 - Still waiting while our PMs, Devs, Clients and some Aliens complain about the lines, that noone, not even the source, has a solution for.

    Friday, August 16, 2019 12:50 PM
  • It is now May 25 2020 and they still have not done anything about this bug.

    @Microsoft instead of adding new features to Outlook why don't you actually fix serious bugs like this that have wasted and continued to waste countless developer hours trying to work around your stupid bugs?!

    I literally have a fresh brand new version of Outlook from O365 and this bug is still there.

    @Microsoft Every time you let bugs like this continue to persist without a resolution and waste more developers time trying to work around it, the developer community continues to  lose faith in you. I personally as a result of lingering issues like this, refuse to use any Microsoft Software and SaaS/PaaS or any other offerings.

    Monday, May 25, 2020 8:10 AM
  • Hi,

    I too have seen this issue in my Outlook emails I send out.
    I decided to do some testing tonight.

    If you prepare your html and open the .html file in MS Word you should be able to reproduce the error quickly.
    In my case I had an HTML table and if I resize it vertically using the corner of the table you can see the white lines appear and disappear. You could decide save this updated HTML from MS Word but they add a lot of unnecessary code and it my case I create the email HTML code dynamically form another system, so this was not an option.

    I found that if I set this code in HEAD section of the HTML:

    <style type="text/css"> 
    table { 
    border-collapse: collapse; 
    border-spacing: 0; 
    z-index: 1000;

    table tr { 
    table td { 


    And I also set my font to PT instead of PX the issue has seemed to go away.

    TD and TH html style has padding:3pt; and font-size:12pt;

    Anyway Microsoft need to look at their MS Word HTML engine because that is where this bug is.

    I have the latest 365 version installed.

    Not sure if this will help anyone but hope so.

    Tuesday, June 9, 2020 7:06 PM