IIS SMTP realy Via EOP geeting 4006 event error just for one external domain

subash shah 11

I am having a strange issue with my SMTP server with delay only to one domain , checked on the IIS SMTP server and finding event ID 4006 , Mail Delivery to the host 104.47.71.138 failed while delivering to remote domain "xyz.com" for the following reason:The connection was dropped by the remote host.

Steps Taken so far:
Telnet fine.
emails get delivered but almost after 2 to 3 hours.
AV was disabled no luck so far.
-Public IP has been checked no blacklist issue.
-Connection filter we have whitelisted the domain and the public IP in EOP still No luck.

Bruce Zhang-MSFT 3,736 Reputation points

2022-02-03T02:00:06.27+00:00
Hi @subash shah ,

I think you can try following method:

Make sure firewall doesn't block port 25. You can temporarily disable the firewall. Check if it can receive emails.

Make sure you have correct Exchange server's FQDN in a Smart Host. Go to IIS Manager -> Default SMTP Virtual Server -> Properties -> Delivery -> Advanced -> Smart Host and check it.

You may want to disable" Internet E-mail Auto-protect" in the Symantec Antivirus Client or disable the antivirus email scanning and to exclude the \Inetpub and %systemroot%\system32\inetsrv from any real time virus scanning.