SMTP error RRS feed

  • Question

  • My application is built with and we are getting an error when we bulk emails through SMTP. We are using <g class="gr_ gr_22 gr-alert gr_spell ContextualSpelling ins-del multiReplace" data-gr-id="22" id="22">appriver</g>  credentials for SMTP userName and password.

    When I am trying to send a series of emails one by one, getting an exception and the details as follow. The exception is coming after few emails have sent

     Syntax error, command unrecognized. The server response was: <User email>  recipients flow control, try later


    Stack Trace: 
    at System.Net.Mail.RecipientCommand.CheckResponse(SmtpStatusCode statusCode, String response)     at System.Net.Mail.SmtpTransport.SendMail(MailAddress sender, MailAddressCollection recipients, String deliveryNotify, SmtpFailedRecipientException& exception)     at System.Net.Mail.SmtpClient.Send(MailMessage message)     at LeapSeedCommon.Utilities.Mailer.SendHTMLMailMessage(String mailFrom, String mailToName, String mailSubject, String mailBody, ReaderProvider rpLocal, String mailCcName, String mailBccName, Attachment& oAttachment)     at ASP.portal_admin_donor_names_filemanager_email_donor_names_aspx.btnEmailSend_Click(Object sender, EventArgs e)

    Please let me know that why this issue happening and suggest a solution.

    Tuesday, March 17, 2015 9:12 AM

All replies

  • Hi Sareen,

    This might be due to Exchange Workload Management Throttling.

    Get it checked by your Exchange Admin.


    Throttling functionality is enhanced in Exchange 2013. The enhanced functionality helps make sure that excessive resource consumption by individual users doesn’t adversely affect server performance or the user experience.

    By default, user throttling in Exchange 2013 allows users to increase resource consumption for short periods without experiencing any reduction in bandwidth. Also, the complete lockout of users who use a very large amount of resources will be infrequent, or never occur. Rather than completely blocking a user from performing operations, throttling occurs and processes are delayed for short periods of time (think of them as "microdelays"), occurring before they cause a significant impact on a server.

    Read below article for more details:

    Exchange workload management

    Various Parameters available to throttle individual or all users:


    The MessageRateLimit parameter specifies the number of messages per minute that can be submitted to transport. For messages submitted through the Mailbox server role (using Microsoft Outlook, Microsoft Office Outlook Web App, Exchange ActiveSync, or Exchange Web Services), this results in the deferral of messages until the quota for the user is available. Specifically, messages appear in the Outbox or Drafts folder for longer periods of time when users submit messages at a rate greater than the MessageRateLimit parameter.



    Please “Vote As Helpful” if you find my contribution useful or “Mark As Answer” if it does answer your question. That will encourage me - and others - to take time out to help you.

    Tuesday, March 17, 2015 12:08 PM