IIS 5 & IIS 6
SMTP Relay suddenly sending multiple copies of email
Last post Oct 11, 2018 11:13 PM by jhickman
Sep 25, 2018 11:07 PM|Timothy D K 1972|LINK
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
firstname.lastname@example.org, email@example.com, and
firstname.lastname@example.org 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.
Sep 26, 2018 03:29 PM|DShoemaker|LINK
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/
Oct 02, 2018 03:58 PM|Roger Capone|LINK
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.
Oct 08, 2018 08:20 AM|Fred_31|LINK
I have the same problem since mid september.
Oct 11, 2018 11:13 PM|jhickman|LINK
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.