Duplicating The Use Of "X-Unsent: 1"

Discussion of general topics about Mozilla Thunderbird

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Posts: 59
Joined: February 5th, 2006, 1:09 pm

Post Posted June 7th, 2018, 10:38 am

Many years ago, I discovered this simple headers:
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X-Unsent: 1
If included in a file that the default mail application was set to open, would cause the mail application to open the message in "draft mode", where as you could edit the message more, or add more people to the "To:" field, etc, etc, before hitting the Send button.

That wonderful time saver enabled me to use:
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ShellExecute 0, "Open", Filename, "", "", 1
In my VBA applications to send a message file that was constructed with the VBA.

Alas, TB does not honor that header. Bummer.

It's used in hundreds of Excel workbooks which need to generate a custom HTML formatted message for the SendTo.

Serious bummer. ... hunderbird
Okies, I could do that. ... 21(v=vs.85).aspx
I could also do that.

But not now, I need a quick solution. Mainly because I need something that I can drag and drop, or use a secondary interceptor within the "open" command for the ShellExecute to handle the conversion from .EML to command line formatting or something.

But the biggest issue is that I worked a nice little (HA!) macro that took a single worksheet and subdivided it into several .CSV files, IN MEMORY, converted them to Mime64, and built an email with that.
(Code available to any who want to see how it works.)

Oh boi.

Short of hacking the registry or doing weird (and possibly unacceptable) things to the OS, any other suggestions?


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Joined: July 30th, 2003, 5:06 pm

Post Posted June 29th, 2018, 3:36 pm

So you are trying to open a .eml file that has a "X-Unsent: 1" header in Thunderbird, and get it to display that message in the compose message window? That's pretty Microsoft specific behavior for a cross platform application. Thunderbird doesn't treat .eml files as first class citizens. Thunderbird doesn't rely upon the windows registry as much as most Windows applications, which rules out many registry hacks.

If its too time consuming to modify the arguments to ShellExecute to use the command line arguments that Thunderbird supports that also rules out using SimpleMAPI calls as an alternative. There is a ExternalEditor add-on at . See the second comment for a link to the latest version.

I did find (Add support for X-Unsent property in .eml files) . A duplicate bug report (with its own discussion) is at . See if the discussion in those bug reports gives you any ideas. I found a reference to an add-on at ... t-support/ that claims to do what you want for Thunderbird. Its not clear why its listed under Firefox add-ons. seems to be what you want. See and if there are issues with it.


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Posts: 59
Joined: February 5th, 2006, 1:09 pm

Post Posted July 9th, 2018, 1:17 pm

Can be found in Thunderbird's search for addons, and will install from there.

Thanks dude, this was just needed.

It's the dozens of existing calls in my system that are the ankle biters here.

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