The IMail SMTP service hangs in a StopPending state and the process cannot be killed even through task manager.

This issue appears to be caused by a recent update by Microsoft for the .NET framework.   To correct the issue,  you can either remove the problematic .NET security roll up OR install the optional .NET 4.7.2 upgrade.

Updated 7/20/18: Due to sporadic ongoing issues even after Installing .NET 4.7.2, we are now recommending Option 2, Removal of the 2018-07 Security and Quality Rollup.

Option 1 :  Install Microsoft .NET Framework 4.7.2

• * From your server, navigate to "Windows Update"
• * Click the link for "Important" updates.
• * Locate the item "Microsoft .NET Framework 4.7.2" and tell Windows Update to install it.
• * Restart Windows when prompted at the end of the installation.

Option 2 (Recommended): Remove 2018-07 Security and Quality Rollup for .Net Framework

• * From your server, navigate to "Windows Update"
• * Select the option to "View Update History"
• * Confirm that the "2018-07 Security and Quality Rollup for .Net Framework" has been installed.
• * If so, at the top of the screen click the link for "Installed Updates".
• * Select any Microsoft.NET Framework updates that were installed in July 2018 and click Uninstall.
• * You may be asked to reboot to apply the changes.