SMTP Relay suddenly sending multiple copies of email RRS feed

  • Question

  • User-138460925 posted

    We are using IIS 6 SMTP relay to route mail through O365 for a few applications.  Have been doing so for 2 years with no trouble but recently, the SMTP relay has started sending multiple copies of an email if the recipients are in different email domains.  For example, one email has 3 recipients and they are jim@gmail.com, tom@outlook.com, and sarah@hotmail.com since they each have a different email domain, the relay server is sending it 3 times.  In the logging, you can see the relay open a new connection to O365 for each email domain and send the message.  Started happening around the Sept 13th 2018 timeframe.

    Tuesday, September 25, 2018 11:07 PM

All replies

  • User-605284035 posted


    We are experiencing exactly the same issues. Also using IIS 6.0 SMTP relay to route mail.

    No recent changes, and duplicate emails were noticed on the 14th of September 2018 for us.

    Same experience with the different domains.

    We've opened a support ticket with Microsoft but have not had any luck yet.

    Any success for your team with a resolution yet?



    Edit; Found this link too: https://www.reddit.com/r/sysadmin/comments/9hqrbj/duplicate_emails_coming_from_iis_relay_to_o365/

    Wednesday, September 26, 2018 3:29 PM
  • User505866979 posted

    We have a similar issue sending out SSRS subscription emails via our SMTP relay that started on or about 9/12/2018. Each recipient receives duplicate emails depending on the number of different domains are sent to. If the email only goes to 1 domain, only 1 copy is received by each person. If there are 5 different domains in the list, each person gets 5 copies. Our SMTP logs only show 1 copy being sent, but Office 365 message traces show the multiple emails with the same message ID, but usually different Office 365 servers. I've opened a ticket with Office 365 support (11584906) and have been monitoring this thread: https://www.reddit.com/r/sysadmin/comments/9hqrbj/duplicate_emails_coming_from_iis_relay_to_o365/?sort=new, but still no resolution. 

    Tuesday, October 2, 2018 3:58 PM
  • User-287533368 posted

    I have the same problem since mid september.

    Monday, October 8, 2018 8:20 AM
  • User1795052663 posted

    This is exactly whats happening for us too. SSRS subscriptions sent through SMTP via O365 are being received multiple times, I didn't realise it was based on the number of domains but I have checked that this is the case for us too. We noticed this on the 9th of October, however its possible this has been happening longer than that.

    Thursday, October 11, 2018 11:13 PM