SendGrid emails intermittently failing with "406 Not Acceptable"

I’m using the built-in Auth0 SendGrid integration for email sending, and I’m seeing a significant chunk (right now, maybe 30%) of SendGrid emails failing to send recently.

The email provider test emails do work fine, so my configuration seems correct in general, but passwordless login emails intermittently do not.

This is quite a major issue for me, as with passwordless it means many of my users are locked out entirely!

Can somebody please look into this? There’s an example error here:

The main error message there says:

SyntaxError: Unexpected token < in JSON at position 0 JSONPARSEERROR when parsing: <html>\r\n<head><title>406 Not Acceptable</title></head>\r\n<body bgcolor=\"white\">\r\n<center><h1>406 Not Acceptable</h1></center>\r\n<hr><center>nginx</center>\r\n</body>\r\n</html>\r\n

If this is an issue with SendGrid, please let me know what is wrong, and I’ll get in touch with them. Their docs say this response will only appear when an API request sends an incorrect Accept header though, and given that it sounds more likely that Auth0 is sending incorrect parameters for requests in these cases.


Hey @pimterry! Thanks for reporting this. I’m investigating this, stay tuned.


Any update here? We are getting the same issues

I’m sure Art will follow up on that once he finish his investigation. Thank you for patience Amit!

@konrad.sopala I’ve also been in touch with developer support directly, who’ve confirmed they’ve seen this issue too and that the engineering team are working on it.

Given that this is a confirmed & widespread intermittent failure of core functionality, why isn’t this shown as an outage on

Right now that page says all systems are operational, whilst many of my users are reporting that it’s impossible to log in (because I use passwordless login, which depends on email delivery).

It would be useful if the status page accurately reflected system issues like this. I’d much rather have heard about the issue from there, rather than complaints from my end users.

Hey all,

My apologies, it’s taking longer than I expected. The issue seems to be elusive and tracking it got tricky. From what we know now, it seems to be an issue with SendGrid and could very well be out of our immediate control, and we are working with their support team to help us figure it out. Please rest assured I’m on it and will update you as soon as I have more information.

P.S. At the time of this posting, we see no indications of any issues with SendGrid. We’ve setup a few extra alerts specific to this and will be tracking this closely.

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Thanks for the headsup Art!

Hi, bad news, I have tried using a different SMTP provider - Google SMTP/Gmail. The exact same problem occurs, I can receive all other email templates apart from blocked_account and stolen_credentials.

There is no sight of those problem emails in the SMTP logs in Google, but every other one is there.

The problem seems to be wider than just with SendGrid


Are there further updates on this issue?

I am also using SendGrid integration for email sending, and I am intermittently getting the same error as @pimterry is having:

"SyntaxError: Unexpected token < in JSON at position 0 JSONPARSEERROR when parsing: <html>\r\n<head><title>406 Not Acceptable</title></head>\r\n<body bgcolor=\"white\">\r\n<center><h1>406 Not Acceptable</h1></center>\r\n<hr><center>nginx</center>\r\n</body>\r\n</html>\r\n"

This effectively locks out users outside of our organization.

Looks like SendGrid had an incident yesterday:

Please let me know if you are still experiencing this.


Thanks for the heads-up Art!