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  3. Too many concurrent SMTP connections

Too many concurrent SMTP connections

Scheduled Pinned Locked Moved Solved Mattermost
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    • T Offline
      T Offline
      tomw
      wrote on last edited by
      #1

      Hi everyone,

      I am using the Cloudron built-in SMTP server for the domain Mattermost sends email from and I just noticed in my logs that when sending a notification email to many users at once (e.g. resulting from an @all) , lots of them fail with an error like the following:

      {"level":"error","ts":1614543114.932735,"caller":"app/notification_email.go:105","msg":"Error while sending the email","user_email":"[DELETED]","error":"SendMail: Failed to open TLS connection., 421 Too many concurrent connections"}
      

      It looks like Mattermost tries to send all the emails at once and there is no retry logic, so the result of this is that only a fraction of the users will receive the notification emails that are expected. There is an upstream bug to add a configurable maximum number of connections that has been open since 2016.

      I guess when using an external mail service, the large number of concurrent connections may not be a problem. For example, Sendgrid states that up to 10,000 concurrent connections from a single server are permitted.

      However if possible I would like to stick with the built-in SMTP server so that it is not necessary to pass this data through a third party. In my case there are around 60 people in the Mattermost team, so that should be the theoretical maximum number of emails being sent simultaneously.

      I am wondering if it would be practical to bump up the number of simultaneous connections allowed by the built-in SMTP server to 60 without causing problems? Or if anyone has any other ideas for a way around this problem?

      Tom

      girishG 1 Reply Last reply
      0
      • T tomw

        Hi everyone,

        I am using the Cloudron built-in SMTP server for the domain Mattermost sends email from and I just noticed in my logs that when sending a notification email to many users at once (e.g. resulting from an @all) , lots of them fail with an error like the following:

        {"level":"error","ts":1614543114.932735,"caller":"app/notification_email.go:105","msg":"Error while sending the email","user_email":"[DELETED]","error":"SendMail: Failed to open TLS connection., 421 Too many concurrent connections"}
        

        It looks like Mattermost tries to send all the emails at once and there is no retry logic, so the result of this is that only a fraction of the users will receive the notification emails that are expected. There is an upstream bug to add a configurable maximum number of connections that has been open since 2016.

        I guess when using an external mail service, the large number of concurrent connections may not be a problem. For example, Sendgrid states that up to 10,000 concurrent connections from a single server are permitted.

        However if possible I would like to stick with the built-in SMTP server so that it is not necessary to pass this data through a third party. In my case there are around 60 people in the Mattermost team, so that should be the theoretical maximum number of emails being sent simultaneously.

        I am wondering if it would be practical to bump up the number of simultaneous connections allowed by the built-in SMTP server to 60 without causing problems? Or if anyone has any other ideas for a way around this problem?

        Tom

        girishG Offline
        girishG Offline
        girish
        Staff
        wrote on last edited by
        #2

        @tomw the concurrency is set quite low at the moment - just 5. There's no issue bumping this value, it was just a very conservative setting.

        As a temporary fix:

        • docker exec -ti mail /bin/bash
        • Edit the file /run/haraka/config/limit.ini. There is a concurrency section under which max is set to 5. Make is say 200.
        • supervisorctl restart haraka

        Does that make things work? The configuration does not survive server restarts, but I will bump it in the next release.

        T 1 Reply Last reply
        0
        • girishG girish

          @tomw the concurrency is set quite low at the moment - just 5. There's no issue bumping this value, it was just a very conservative setting.

          As a temporary fix:

          • docker exec -ti mail /bin/bash
          • Edit the file /run/haraka/config/limit.ini. There is a concurrency section under which max is set to 5. Make is say 200.
          • supervisorctl restart haraka

          Does that make things work? The configuration does not survive server restarts, but I will bump it in the next release.

          T Offline
          T Offline
          tomw
          wrote on last edited by
          #3

          @girish said in Too many concurrent SMTP connections:

          Does that make things work?

          Brilliant, thanks @girish! I have made the change and will report back next time someone sends an @all message.

          T 1 Reply Last reply
          0
          • T tomw

            @girish said in Too many concurrent SMTP connections:

            Does that make things work?

            Brilliant, thanks @girish! I have made the change and will report back next time someone sends an @all message.

            T Offline
            T Offline
            tomw
            wrote on last edited by
            #4

            Update: We have successfully triggered emails with an @all to 46 people without errors, so the fix seems to have worked. 👍

            girishG 1 Reply Last reply
            1
            • T tomw

              Update: We have successfully triggered emails with an @all to 46 people without errors, so the fix seems to have worked. 👍

              girishG Offline
              girishG Offline
              girish
              Staff
              wrote on last edited by
              #5

              @tomw thanks for the update! I will make the default value higher in the next release.

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