[release/8.0] fix redundant CRLF response during SMTP negotiate #109112
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Backport of #105939 to release/8.0-staging.
Fixes #108382
/cc @rzikm @avin3sh
Customer Impact
Reported by a customer (financial institution) as migration blocker from .NET Framework to .NET Core LTS version. They need 8.0 LTS due to internal security restrictions.
The problem is with SMTP Negotiate authentication response, which is incorrect (reached via SmtpClient).
Regression
Yes - between .NET Framework and .NET Core.
It did not work on recent .NET Core releases. Possibly broken about 8 years ago when introducing Unix support.
Testing
Patch submitted and tested by customer - confirmed in #108382 (comment)
Risk
Low, the change is very contained and relevant code paths have been tested.