Issue with Incoming email - "Unable to deliver message. No such domain"

Here is the case, we were so confident with our SMTP configuration and users were happy except one , you will come to know WHY??

We had enabled incoming email option for a library and so we have communicated users with the appropriate email address for that library.E.g.: Reports@lib.org.com. Users were able to send and receive emails to the SharePoint library. Same we have tested from our end.

The other user had reported and emailed me with the supporting error messages. It clearly says "Unable to deliver message. No such domain", which is not true. We are able to receive emails in the library still.

User has sent an email with the attachment of 16 MB file to the correct email address and a bounce back email with the above error in his inbox(Same for us - admin). To the same email address, if we sent an email with/without attachment but of size less than 10 MB, we were able to see emails in the document library.

From the server end, the file didn't reached the DROP(C:\inetpub\mailroot\Drop) folder in the email configured SharePoint Server. Whereas the other files received in QUEUE, then DROP and updated perfectly in the site.

You can check your email header, in my case it clearly says that the file was not out of Exchange. To access email header, open your delivery status email→File→Info→Properties, here you can see internet header, where you can track your email.

The issue is now narrow downed to Email size, since we were able to send email less than 10 MB and not the 16 MB file. Its is already out of my email box and struck with exchange(got it from header). so nothing to do with my mail box.

Again into the SMTP configured SharePoint Server and looking to change the email size limit. Open IIS 6.0 not the IIS manager to check SMTP properties, expand server name and right click on the SMTP virtual server→On properties Window → Under "Message" tab you will see limit information.

I changed it to maximum size but still no luck in fixing this issue.

There is someting called Send Connector, through which emails can sent to SharePoint server. By default it would be 10 MB. Working with Exchange team, from exchange management console, we changed the default value to 20 MB. Wait for 2 to 3 hrs and worked for me!!

Email Success and Happy users 😃