Note that SMTP + TLS is not at port 443...
Actually there is no way to do it on vCenter.
A possible solution is to install in the vCenter Server the SMTP component of Windows Server, configure it to do relay for localhost and to use SMTP + TLS.
Then configure vCenter to use localhost as a SMTP server.
If you are using Exchange as email server you can just create a new receive connector for vCenter without TLS. The email will staty local anyway.
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