I just found out about the staged users ability and yes, it’s a nice feature! thanks for the suggestion 
a question regarding this method:
it’s like asking people to send an email to test@test.com in order to contact us. the only difference would be that we receive their response in the platform rather than our email.
isn’t it?
I’d like the users to be able to contact us via the platform itself.
Any way to open the Email Composer w/o having to fill in the user? e.g.
https://discourse.domain.org/new-message
vs. having to fill in a user
https://discourse.domain.org/new-message?username=user_name
Use-case is a simple bookmark to composing PMs.
And there is no way to PM a user starting from an email, like we can create a Topic post from email, correct?
Hmm, at least some form of the empty version should work @techapj
https://meta.discourse.org/new-message?username=
Okay, this is now done via:
All of the below format will work now:
https://meta.discourse.org/new-message
https://meta.discourse.org/new-message?username=
https://meta.discourse.org/new-message?title=foo&body=bar
https://meta.discourse.org/new-message?groupname=Nice. Pulled from tests-passed, and it looks great!
Hi, this looks great but limited because I am not able to get the following format to work if the message is to a group:
https://meta.discourse.org/new-message?username=
The composer is not opening up if the username is a group… (whereas it does to a single user)
one other comment/request - if it’s a new message can it open up with the /my/messages page in the background?
What you are looking for is https://meta.discourse.org/new-message?groupname=
Notice username vs groupname parameter. Also make sure that the group is messageable.
It doesn’t as of now, but a PR for this change is certainly welcome. 
Hello. I was wondering if there are any updates regarding having multiple users within the link to create a message? Note that these multiple users are not all in a group. Thank you!
This feature doesn’t exist as of now. A PR for the same is certainly welcome.
Great work! Is there any existing trick to allow an e-mail address in username like this?
discourse.example.com/new-message?username=john@example.com&title=message%20title&body=message%20body
This returns an error right now but supporting it might help sending e-mails from a Discourse instance.
Email address is not supported yet. I’ll add it on my longer term to-do list. 
Is it possible to also actually send the PM using a command in the URL?
The use-case is in attempting to launch the @discobot tutorial with a single click. At the moment, it is straightforward to use a URL to create a PM with the correct text in it, but the user must also click on ‘Message’ the fire it up. A minor point, but this will be used by very green users for whom every click counts.
No that is not possible and is not planned. It would be a massive security issue for what I hope are obvious reasons.
Thank you - fair enough; it would indeed be a security issue if a malicious user worked it out.
Including some text to prompt them to hit the “Message” button in the message would address this issue anyway as per:
Does anyone happen to know if this has been implemented since Aug '16? Or is there some other url that can be used to open a private message composer on the user’s profile? I couldn’t reach a conclusive answer from some light skimming over the code.
Hello thanks for this expliction but how to add variable “%{post_url}”, for exemple, in URL ?
Thanks