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Hi,
kindly help anyone with my public IP can connect to my exchange server and send email to anyone within our domain, I have tried to configure smtp relay but the problem is still there.
Thanks
A
Thats by design and how SMTP works.
Thanks @Andy David - MVP for your response, it means there is no way to protect above issue?
No because using telnet on port 25 is the same as a mail server sending the message.
Your anti-spam/ anti-malware solution is the key to prevent abuse.
Like adding any type of auth so that you can protect anyone from spamming.
Thanks again @Andy David - MVP , which anti-spam/ anti-malware solution would you suggest
You can't require authentication for external mail servers, otherwise you wont get any mail from the internet :)
Personally, I would use a 3rd party cloud based solution and route inbound to that and then to your on-prem Exch Server
EOP, Proofpoint, Mimecast etc...
Thanks A lot @Andy David - MVP