Why does Thunderbird add ‘\A0’ and other strange-looking strings in e-mails I send?

I use Linux and have used the Thunderbird e-mail client since 2008. I used to use DavMail to enable Thunderbird to access various company Microsoft Exchange WebMail accounts but, several years ago, DavMail would no longer work with a particular Microsoft Exchange account so I switched to the Thunderbird add-on ExQuilla, for which I pay an annual licence fee. I do not know if the more recent versions of DavMail would work with this particular account but ExQuilla got me out of a hole so I stuck with it. Recently this particular corporation decided to stop using an in-house Microsoft Exchange server and switched to Microsoft 365.

Recently people receiving my e-mails sent using this particular account told me there were strange strings of characters in e-mails of mine that quote other e-mails. The most frequent occurrence is the three-character string ‘\A0’, although other strings are sometimes present too. The following e-mail extract illustrates the effect:

Hi Claudia,

I have had a look at your draft and agree with your assessment. Let’s sit down together and prepare a list of possible remedial measures.


On 07/10/2020 13:02, Claudia wrote:
> Hi,
> \A0
> Could you please have a look at the draft I have attached.
> \A0
> There are several main issues requiring attention. The operation was basically run by one person \2013 (John) during the tests, which led to several issues.
> \A0
> He does not have the time to do everything by himself.\A0 The other staff who had assisted him during earlier tests were not present.

Notice various occurrences of ‘\A0’ and an occurrence of ‘\2013’.

I searched the Web to see if other Thunderbird users had come across this problem, and found several reports of similar problems, although not identical. The most promising page I found was in the Mozilla support forums for Thunderbird: Why do my sent messages magically add “�” at the end of my sentences?. However, none of the various fixes suggested in that thread worked in my case. My Thunderbird installation was configured to use ‘Unicode (UTF-8)’ text encoding for Outgoing Mail and Western (ISO-8859-1) for Incoming Mail ( ‘Edit’ > ‘Preferences’ > ‘General’ > ‘Language & Appearance’ > ‘Advanced…’ > ‘Text Encoding’). I changed the text encoding for incoming mail to ‘Unicode (UTF-8)’ but that made no difference. I ticked ‘When possible, use the default text encoding in replies’ but that also made no difference. Anyway, I left the settings like that and hoped an update to Thunderbird would fix the issue.

I was not sure if the problem started with an upgrade to Thunderbird, or whether the switch to Microsoft 365 was the cause. I suspect Microsoft 365 is the culprit because the problem does not occur when I use other e-mail accounts. Anyway, it is annoying and I have still not found a fix for it. One of the replies in the above-mentioned Thunderbird support thread is not identical to what I’m seeing, but it looks to be essentially the same problem:

Jorg K
2/4/18, 6:17 AM

There is NO bug in Thunderbird. Sadly some US ISP’s like AT&T and Bellsouth have started *corrupting* their customers’ e-mail.

If the customer sends in windows-1252 and includes for example special punctuation characters or a non-break space xA0, the ISP doesn’t correctly interpret the the message as windows-1252 but as UTF-8. In UTF-8, xA0 is not valid and gets replaced by the so-called replacement character, � (0xEF 0xBF 0xBD).

Since the e-mail is still windows-1252 encoded, the recipient’s client displays �.


Affected users should complain heavily to their mail providers. As a workaround, they need to send all messages as UTF-8.

This seems to be a possible explanation of what I am experiencing, but it is impractical for me to check what text encoding all my contacts are using, or get them to switch to UTF-8 if they are not already using it in their e-mails. I noticed that there is actually a space in what look like blank lines in the e-mails I quote, and, if I delete that space, the ‘\A0’ no longer appears on those lines when I view the contents of e-mails in the Sent Items mailbox. I think that the space is, in fact, a non-breaking space (xA0), which is apparently invalid in UTF-8 and gets displayed as ‘\A0’ by Thunderbird (I’m currently using Version 78.4.2).

Trying to find and delete all the non-breaking spaces and other non-UTF-8 characters in a quoted e-mail is impractical. However, I found a somewhat cumbersome work-around to the problem of non-breaking spaces (and, I think, other non UTF-8 characters). When I click on the ‘Reply’ button in Thunderbird and a window pops up for me to compose my reply which includes a quoted e-mail or e-mails, I use Ctrl-C to copy all the contents of the window, then Ctrl-V to paste it back into the window. This seems to get rid of the character strings representing non-UTF-8 characters. It does add some extra blank lines in the quoted e-mail(s) in the window in which I am composing my e-mail, but those extra blank lines are normally not present when viewing the e-mail after it has been sent.

This work-around is not ideal as it relies on me remembering to do it when composing an e-mail in which I am quoting a previous e-mail or e-mails. But at least it gets rid of the multiple additional occurrences of ‘\A0’ (non-breaking space). It’s a pity there is no mechanism in Thunderbird to filter out non-UTF-8 characters such as a non-breaking space when quoting other e-mails. Even if Jorg K in the above-mentioned thread is correct and the cause of the problem does not lie in Thunderbird, I would rather Thunderbird act differently if the user has configured it to send e-mails using UTF-8 text encoding, and filter out non-UTF-8 characters rather than including strings of gobbledygook in the e-mail.

About Fitzcarraldo
A Linux user with an interest in all things technical.

8 Responses to Why does Thunderbird add ‘\A0’ and other strange-looking strings in e-mails I send?

  1. Thomas says:

    I’m having this same issue also with \A0 with ExQuilla and Thunderbird on Windows and haven’t found a solution yet. Thanks for the copy-paste workaround

  2. Fitzcarraldo says:

    Apparently the problem is caused by the ExQuilla add-on:


    This is a known issue that we’re working on. Please try using Thunderbird 68.x for the time being. It should be fine there.


    ExQuilla support

    Beonex GmbH
    Wiesbaden, Germany
    CEO / Geschäftsführer: Ben Bucksch
    Handelsregister: Amtsgericht Wiesbaden, HRB 30065

  3. Beonex says:

    This is Beonex. This issue is actually caused by a bug in Thunderbird, specifically bug https://bugzilla.mozilla.org/show_bug.cgi?id=1675507 . This bug makes Thunderbird send invalid HTML. That invalid HTML then makes the Exchange server insert these A0. This is why you see it only with ExQuilla. But that’s not the fault of Exchange nor ExQuilla, but of Thunderbird that generated invalid HTML.

    A fix is in progress.

  4. Fitzcarraldo says:

    Just in case other people are wondering what other strange-looking strings appear in Thunderbird using ExQuilla when quoting e-mails from others in an e-mail, I have come across the following so far in my e-mails in which I have quoted other people’s e-mails. Some (all?) of those people are using Microsoft Outlook and Office 365, as far as I know:

    \A0 is a substitute for a non-breaking space.
    \2013 is a substitute for an en dash.
    \2019 is a substitute for a right single quotation mark.
    \2026 is a horizontal ellipsis.

    See https://en.wikipedia.org/wiki/List_of_Unicode_characters

  5. Andy says:

    Really useful thread, thanks. I have the same issue with Exquilla and recipients in Office365 (in some of its platforms – browser is main culprit I think)

    In addition some forwarded messages appear completely blank to the recipient. Anyone know a workaround?

    • Fitzcarraldo says:

      The problem with forwarded e-mails appearing blank is also due to Mozilla Thunderbird bug 1675507. Perhaps the latest release of ExQuilla (Version 78.0.6) that contains a work-around for that Thunderbird bug, to avoid strings such as ‘\A0’ in quoted e-mails, will also fix that problem with forwarded e-mails.

  6. Fitzcarraldo says:

    Thunderbird on my laptop running Gentoo Linux today received an automatic update to ExQuilla. The ExQuilla release notes (Tools > Add-ons > Manage) state the following:

    * Workaround for Thunderbird bug 1675507 that causes “\A0” to appear in sent mail.
    * Support RedirectAddr in AutoDiscover during setup.
    * Fix setup when AutoDiscover supports BasicAuth, but EWS (mail check) does not.
    * Workaround for Thunderbird bug 1682309 that causes error message ‘JavaScript component does not have a method named: “OnStartRunningUrl”‘.

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