",
"subject": "Email Deliverability Test"
},
"attachments": [],
"size": 7127
},
"recipient": "[recipient user]@[recipient-domain]",
"event": "failed"
}
```
Quoting ticket reply from Mailgun:
> The error that you are seeing is the result of sender address verification, and you can read more about it in the following link: [Callback verification - Wikipedia](http://en.wikipedia.org/wiki/Callback_verification). Essentially, this means the recipient domain is performing a check to make sure the sending address is valid.
>
> The following options will help you resolve this error:
>
> 1. Turn off sender address verification (this is server-side).
> 2. Add “x-mailgun-native-send: true” to the header of your message to turn off sender address rewriting.
> 3. Send from a subdomain of your domain.
> 4. Change the MX records to point to Mailgun instead. ( **Warning** : do not do this unless you have a Route setup to route back to the internal server.)
> 5. Create a catch\_all with the service where you receive email so that, when the recipient server checks, verification it will pass.
Any one has any suggestions on this?
Thanks a lot!
Daniel
---
### Author:  [@itsbhanusharma](https://meta.discourse.org/u/itsbhanusharma)
#### Post date: [August 24, 2018, 10:15am UTC](https://meta.discourse.org/t/550-verification-failed-no-such-user-callback-verification/95560/2 "2018-08-24T10:15:23Z")
I see that you have enabled cloudflare on your mx records as well!
Can you try again by disabling cloudflare on your mx domain/subdomain?
I Noticed your forum runs on http not https is there a purpose for that?
---
### Author:  [@dexpositoromero](https://meta.discourse.org/u/dexpositoromero)
#### Post date: [August 24, 2018, 10:23am UTC](https://meta.discourse.org/t/550-verification-failed-no-such-user-callback-verification/95560/3 "2018-08-24T10:23:17Z")
Right… So it looks like it is fixed now…
Just for future reference from someone having this problem, I just went to **cPanel \> Email Routing** , and for the subdomain I am using for Discourse (and thus the subdomain Mailgun generates the postmaster/no-reply emails) I chose _“Remote Mail Exchanger”_ and click on _“Change”_…
Seems to work now with all emails… 🙄
---
### Author:  [@dexpositoromero](https://meta.discourse.org/u/dexpositoromero)
#### Post date: [August 24, 2018, 10:25am UTC](https://meta.discourse.org/t/550-verification-failed-no-such-user-callback-verification/95560/4 "2018-08-24T10:25:54Z")
Hi Bhanu,
Thanks for your reply. See below, looks like I managed to sort it out.
Re: SSL, because Let’sEncrypt+Cloudflare was a nightmare to set up for the main site, I am using Cloudflare’s shared certificated for the main site. Not sure how to manage it with Cloudflare + Ubuntu, hence why no HTTPS. If you have any links I can look at, that’d be amazing!
Kind Regards,
Daniel
---
### Author:  [@itsbhanusharma](https://meta.discourse.org/u/itsbhanusharma)
#### Post date: [August 24, 2018, 10:28am UTC](https://meta.discourse.org/t/550-verification-failed-no-such-user-callback-verification/95560/5 "2018-08-24T10:28:10Z")
Just disable cloudflare optimization for your forum subdomain and it should in theory be able to generate ssl for you.
---
### Author:  [@codinghorror](https://meta.discourse.org/u/codinghorror)
#### Post date: [August 24, 2018, 10:41am UTC](https://meta.discourse.org/t/550-verification-failed-no-such-user-callback-verification/95560/6 "2018-08-24T10:41:38Z")