Exactly I forgot the exact time of the incident, at that time a friend who infected me suddenly couldn’t send an from Ms. 2007. Worse yet, everyone who uses Ms. Outlook 2007 experienced the same thing from the same server in the same location. If you are looking for this problem, of course, you will find 1001 solutions that are diverse and of course adapted to the problems faced, such as anti-virus, firewall, ISP, SMTP port, Ms. Outlook itself, IP address and other types.

Because of the simultaneous event, my assumption at that time was that the SMTP server was having a problem, I tried restarting it but the results remained the same, I did not try to telnet to the server because it was blocked. Why am I not suspicious of the Public IP? It is also not possible because it uses 2 ISPs, which certainly have different IPs.

So I tried replacing it from “Use same settings …” to “Log on using ….” in the Outgoing Server, of course by using an account from a different domain, and the results are normal.

What’s the matter? the more I was curious about it, finally I tried it with an account that had problems with Ms. 2016, the results are normal. So the problem is, with Ms. Outlook 2007 cannot send with port 465/587 that was previously normal, but with Ms. Outlook 2016 with the same configuration results is normal.

Does the server block Ms. 2007? after searching deeper into the deepest ocean, finally found a part of the solution to that, namely deactivating the configuration in “Requirements for clients to connect with SSL or the STARTTLS issue before they are allowed to authenticate with the server.” send with 587 Auto configuration, the rest still get the same error.

Maybe while this information is what I can give, if I later have the latest info, I will submit it immediately.