smtp-server | Create custom SMTP servers on the fly | Runtime Evironment library

Which language have you provisioned to be returned by the query?

Most probably port number is causing the error and if not, try deleting the mesh policies

Also please validate based on below points:

1.If you recently updated istio try downgrading it. 2.Look again in Sidecar logs for any conflicts or try disabling it. 3.When it comes to curl 56 error packet transmission; limit could be the problem.

The sender information should be inside the headers

Hence, please change the following lines:

After a while, I tried a while more and I've found the solution.

This part is not working

After running some testcases, I have experienced the following:

(This was done by a Outlook.com smtp server.)

• MTA-STS: Deliberately incorrect, but existing third-party mx server in mta-sts file.
• DNS: Correct mx server.

The sender was informed about the delivery failure after 24 hours.

It was explained in my local language what was going on; here information highlights:

1. That the message could was not delivered.
2. That it was tried multiple times to deliver.
3. But that the cause was being unable to connect to the remote server.
4. Advise was given to contact the recipient by phone to ask the recipient to inform the postmaster about the error.
5. It was even suggested that the problem could most likely only be solved by the postmaster.
6. (A link was provided but that wasn't really helpful. Additionally the technical bounce message was visible among it the technical words "failed MTA-STS validation").

• MTA-STS: Correct and desired mx in mta-sts file.
• DNS: Deliberately set to incorrect mx server, existing server though.

After 24 hours I received an error back. Confusingly the message state that the address did not exists in the target domain. Though this is true, it shouldn't have gotten this far. However, when reviewing the technical part the outlook-sending server mentioned 'failed mta-sts errors validation'. So the technical part contained the correct mta-sts validation error, but the human/user readable part only mentioned that the target address did not exist in the target server.

I guess if the address doesn't exists, any mta-sts errors are "less important" to report to the end-user. The user was advised to re-type and resend the e-mail and verify if the address with the recipient (phone was mentioned). However, even if the user followed the instructions, the next e-mail wouldn't have been delivered either, but that is beyond this testcase.

• MTA-STS: Correct mx in mta-sts file.
• DNS: Fake MX corrects.

After 24 hours I received an error back. The cause for not being able to deliver the message was being unable to resolve the domain location of the recipient. (Undesired result, but logical, mx were referring to nothing.)

The technical part of the message mentioned 'DNS query failed'. Nothing of mta-sts was mentioned.

• MTA-STS: Correct mx in mta-sts file.
• DNS: Incorrect but existing mx records; a cname referring to the same IP of the correct mx server (which shouldn't matter because mta-sts should compare cert with cname.)

The results, unexpected:

• One email got delivered somewhere between that 24 time-window.
• One email failed due to mta-sts validation error.

Temporary downtime of webserver might have been a factor, though that shouldn't have mattered. - Cannot explain.

I took a while to find the correct testcase as you can see. But Testcase C describes the desired behaviour. Yes, the sender is informed, after 24 hours with outlook.com as smtp-server. The user is informed in clear language. That being said, I do have an additional opinion about the timing here, mentioned below.

Staying with the facts: I did not perform a testcase with a server trying unencrypted connections. Testcase C puts the ball into the the recipient's postmaster's court, I would be curious to see where the ball (the 'todo') would be placed, in the case of unencrypted attempts, as that cannot be solved by the recipient but must be solved by the sender or sender's postmaster.

I also did not test multiple smtp servers.

That being said, MTA-STS-validation needs to be supported by the sender SMTP (correct me in comments if I am wrong*), so if a server is so old it tries do deliver an e-mail over non-encrypted connection, it will most likely not support MTA-STS so it will not validate the MTA-STS policy and simply deliver the e-mail unprotected. * Found confirmation here, from paragraph "There is a standard...")

If somebody tries to redirect some incoming e-mail by dns-poisoning, a modern smtp-server will not deliver the e-mail to an incorrect destination. So it protects against evil doing, not against legacy.

I think the feedback delay of 24 hours is too long. Testcase C reports 11 retry attempts within that 24 hour window. Though I appreciate the system not giving up, I would argue that it might be in the interest of the sender to inform him of at least a non-regular delivery.

Your servers are not configured to advertise the SMTP authentication extension (RFC 4954), judging from the EHLO response.

The credentials are then not sent by the client (as the server would not understand them anyway).

You should see something like this in the server's response:

So based on what you said you created your own SMTP server which is nice and all to learn, but I would recommend using SendinBlue 3rd party service FREE and gives you 300 mails/day

Getting Started with sendinblue:

• Link: https://www.sendinblue.com/

• Go make and an account free of charge till you decide to pay you'll read there

• Once your account is all set, and activated often SMTP service for ones account is not automatically activate so you'd have to email them and they literally respond within 24hr I LOVE THE SERVICE(I am not promoting nor sponsored to hype them or anything just saying the truth of what I have experienced).

So now at this point your account and SMTP service is activated, now question is how do you use sendinBlue?

• In your dashboard on your Top right you will see your username

• Click on that and a dropdown menu should appear

• Then you want to go to SMTP & API

• Once you then you will see a menu with API Keys on the left and SMTP on the right

• You want to click on the SMTP.

• Once you the you will see Login that would be the email you registered with and you will see Master password now that is what you use to authenticate yourself.

Implementation: Now you have everything sorted you know where you keys are and login

In .env file

You can achieve this by using org.apache.james.smtpserver.netty.SMTPServer. To do this you will need some dependencies.

For Gradle :

If anyone ever faces the same issue, check your settings.py file. It might have trailing commas. This was the issue for me.