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  • Jan Molbech 18 posts 109 karma points
    Sep 14, 2017 @ 11:53
    Jan Molbech
    0

    What does this error mean

    Each day we send out a newsletter and every day some sendout fails.

    We use AWS email service as provider.

    In the newsletter studio backend I've got this errormessage

    Service not available, closing transmission channel. The server response was: Timeout waiting for data from client.
    at System.Net.Mail.MailCommand.CheckResponse(SmtpStatusCode statusCode, String response) at System.Net.Mail.SmtpTransport.SendMail(MailAddress sender, MailAddressCollection recipients, String deliveryNotify, Boolean allowUnicode, SmtpFailedRecipientException& exception) at System.Net.Mail.SmtpClient.Send(MailMessage message) at NewsletterStudio.Services.Mail.NsSmtpClient.Send(MailMessage mail) at NewsletterStudio.Services.SendNewsletterService.SendEmails()

    What does that mean? Is it related to AWS, spamfilter or something else?

    The email adresses that fails, are existing emailadresses that i'm able to send a emailmessage to, hrough a normal email client

  • Markus Johansson 1902 posts 5706 karma points MVP c-trib
    Sep 17, 2017 @ 16:30
    Markus Johansson
    0

    Hi!

    It's an error from the built in .NET e-mail library - it does not come from the Newsletter Studio code.

    When you say "normal email client" do you mean that you can send using the SmtpClient-class in C# och something like Outlook or Gmail?

    It might be that there is something wrong with your SMTP-configuration? Did you configure the server and does it pass the "Test connection"-test?

    enter image description here

    // m

  • Jan Molbech 18 posts 109 karma points
    Sep 25, 2017 @ 07:21
    Jan Molbech
    0

    Hi Markus.

    Each day we send approx. 500 emails. Around 15-20 of them fail, and most of the failed emails have the listed error, so our configuration is functional ("Test connection" is OK).

    With a "normal email client" i menat Outlook and gmail.

  • Markus Johansson 1902 posts 5706 karma points MVP c-trib
    Sep 25, 2017 @ 13:34
    Markus Johansson
    0

    Hi!

    Is it always the same addresses or does that differ?

    The error comes from the .NET SmptClient-class which is out of control of the Newsletter Studio-package.

    But you are sure that all these addresses works in other clients?

    Are you able to send out "test emails" to these addresses?

  • Jan Molbech 18 posts 109 karma points
    Sep 26, 2017 @ 11:58
    Jan Molbech
    0

    The email adresses differ. Yes i'm able to send a test email to the adresses

  • Nik 1591 posts 7148 karma points MVP 6x c-trib
    Sep 25, 2017 @ 13:38
    Nik
    0

    Ontop of Markus's query, there may be a limit into SMTP server that is designed to prevent spam sendings.

    It could be worth checking with them as the error you are referring to indicates that the .NET SMTP client is timing out during the send process when it is waiting for confirmation from the SMTP server itself.

    In the past I've seen this error when too many individual emails have been sent to an SMTP relay that isn't designed for bulk distribution.

  • Craig Mayers 164 posts 508 karma points
    Sep 26, 2017 @ 12:20
    Craig Mayers
    0

    I agree.

    @Jan - What is the total number of emails being sent out from the server?

  • Jan Molbech 18 posts 109 karma points
    Sep 26, 2017 @ 12:29
    Jan Molbech
    0

    We send out around 1K every day. We have a limit of 50 emails/second but we shouldn't hit the limit. We batch the emails in code and limit them to 10 per second.

  • Craig Mayers 164 posts 508 karma points
    Sep 26, 2017 @ 12:37
    Craig Mayers
    0

    Hi Jan,

    Have you checked for any memory leaks from your code? Are you disposing of your objects correctly etc?

    Can we see your code for sending the email?

    Regards

    Craig

  • Jay McGuinness 2 posts 72 karma points
    Sep 26, 2017 @ 13:14
    Jay McGuinness
    0

    We've had this with AWS. Basically EC2 instances are throttled when sending email on port 25.

    https://aws.amazon.com/premiumsupport/knowledge-center/ec2-port-25-throttle/

    So you will encounter sporadic SMTP delivery failures.

    You have two options:

    Hope this helps,

    Jay

  • Markus Johansson 1902 posts 5706 karma points MVP c-trib
    Sep 26, 2017 @ 19:03
    Markus Johansson
    0

    Thanks for helping out on this one Jay!

  • Jan Molbech 18 posts 109 karma points
    Sep 27, 2017 @ 06:05
    Jan Molbech
    0

    We are using port 587. I didn't know that they didn't throttle that port. Then I guess throttling isn't the problem.

  • Jay McGuinness 2 posts 72 karma points
    Sep 27, 2017 @ 15:07
    Jay McGuinness
    0

    Are you using SES? If so, its also worth double checking SES limits:

    http://docs.aws.amazon.com/ses/latest/DeveloperGuide/manage-sending-limits.html

    Good luck!

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