SMTP authentication failed issues

Messaging Service
1

Hi team,

Over the last few months, I’ve been having “authentication failed” issues when sending email. SMTP is configured correctly, and the test is OK, and 98% of all email go through without any issue. However, time and again, I get authentication errors and with the volume of users on my app growing, I am getting these emails increasingly often.

These errors arise in a variety of situations, and the emails I get look like this :

Hello XXX,

This is a notification to inform you about the error by your application.The information about the error can be found below.

Application name: AppName
Application ID: XXX-XXX-XXX-XXX
Message: Error occurred during template-based email sending. Subject '⛵️ Your profile is now up and running!'. Recipients xxx@xxx.com. Email template 'Email verified'
Exception: 535 5.7.8 Error: authentication failed: authentication failed

Thank you for using Backendless!
the Backendless Team

or also

Hello XXX,

This is a notification to inform you about the error by your application.The information about the error can be found below.

Application name: AppName
Application ID: XXX-XXX-XXX-XXX
Message: Send message 'Backendless: zip files' was failed Recipients: xxx@xxx.com
Exception: 535 5.7.8 Error: authentication failed: authentication failed

Thank you for using Backendless!
the Backendless Team

Because this seemed like some problem on the email provider side, I contacted them (Proton) first. They have investigated and been unable to identify a problem on their side. I have several other applications other than Backendless sending email via their SMTP service, and Backendless is the only one triggering authentication issues. Therefore, they told me that

According to our system logs, one possible reason that this occurs on Backendless is because some Backendless email models did not process and send your SMTP credentials to Proton as expected. Can you ask Backendless for their system developer's contact email? We are happy to explain the situation to them, as their developer must retrieve the SMTP logs for further investigation.

Thanks a lot of you could come back to me so that we may find a solution. Indeed, I need to solve this because in the meantime, several of my users are having a poor experience. Some of them, for example, are not getting their address confirmation links, and remain stuck.

Best regards

2

I’ve created the inner task for deeper investigation.
But it sounds quite strange. It would be understandable if the authentication doesn’t work all the time, but you said that it happens sporadically (2%).

  • Provide your appId, please.
  • Clarify, did you try to play with SSL/TLS connections?
  • What type of auth do you use on Proton side: password / token?
4

Hi Oleg,

My appId is D7075715-5086-625A-FFAB-39C2F40FB200.

Can you be more specific as to what you mean “plan with SSL/TLS connections” ? It is set as TLS in Security, and the port used is 587, as per the recommendations here : How to set up SMTP to use business applications or devices with Proton Mail | Proton . It say that “if STARTTLS isn’t available, TLS is the next best option.”

The authentication is also done as specified on this page : I log in to my account, and create an application-specific token, which is used alongside with my email address.

5

Thanks. This info may be helpful in starting investigation of the problem.
When our developers have new information they will post here.

1 Like
6

Hi,

Have you been able to contact the Proton team ? They have sent me a reminder regarding the described issue. I will point them here so that they know the ticket is being worked on.

7

Hi Nicolas,

Please ask your Proton contact to share whatever information they have from their side with support@backendless.com.

Regards,
Mark

1 Like
8

Got it, thanks Mark.

9

Hi,

I was wondering if you had had a chance to dig into this issue ?

I keep having similar issues, and I just had another one just today. Had I not spotted it and resent the email manually, my user would not have been able to confirm their email address.

On October 23rd, the Proton team sent you two messages with technical details. Has there been any update since ?

10

Hello @Nicolas_REMY,

we just checked and can’t find the messages from the Proton team. We’ve checked in the Income, Spam, and Bin folders. Is it possible to ask them to duplicate these messages?

11

Hi,

I just forwarded their email so you have all the detailed information at support@backendless.com.

12

Hi @Nicolas_REMY,

Thank you. We have received your email and will continue to investigate the issue.

Regards,
Viktor

13

We investigated the problem you desribed on our side again.
According to our logs – the user name and password, and the smtp server are the same as for the successful sending and erroneous.
The response from Proton server is the same as from the Proton support you sent: they both say that the provided credentials are wrong. But in this case, you would receive an error message every time you send an email, not only in 1-2%.

We have an assumption, that the error may be from one of the failing (maybe for short period of time) Proton server. The domain name of Proton’s smtp server hides three ip addresses. And for every smtp connection the arbitrary ip is returned. We will add additional logging in order to check this case.