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

subash shah 11 Reputation points

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 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.

Internet Information Services
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