We have just installed a test SQL Server 2016 server on a Windows 2016 standard server. Needless to say, we brought it up to date with SP1 and CU1.
Database Mail was configured as per usual and on testing, it didn't work. No mails were sent. It worked with a previous SQL Server 2016 server. It also had SP1 but CU1 wasn't yet available.
This is from Cumulative Update 1 for SQL Server 2016 SP1 [https://support.microsoft.com/en-us/help/3208177]
Note After you apply this update, Database Mail does not work on computers that do not have the .NET Framework 3.5 installed. Microsoft is currently working on addressing this in a future cumulative update. See the following KB article for more information about affected builds and suggested workarounds
There is a suggested fix: https://support.microsoft.com/en-us/help/3186435/fix-sql-server-2016-database-mail-does-not-work-on-a-computer-that-does-not-have-the-.net-framework-3.5-installed
FIX: SQL Server 2016 Database Mail does not work on a computer that does not have the .NET Framework 3.5 installed
Assume that you install Microsoft SQL Server 2016 on a computer that has the .NET Framework 4.6.1 installed. If the computer does not have the .NET Framework 3.5 installed, the Database Mail feature does not work correctly. For example, if you configure and send a test email message, the message is queued but is never sent.
Note This issue also affects instances that are running SQL Server 2016 SP1 CU1. Microsoft is currently working on a fix that will be made available in a future cumulative update. This KB article will be updated with the relevant information when the fix becomes available.
This problem was fixed in the following cumulative updates for SQL Server: Cumulative Update 2 for SQL Server 2016 (an earlier CU, btw)
To work around this issue, manually install the .NET Framework 3.5.
Is it wise to apply patches and CU2 out of historical order? I am loath to do it. It has anyway been installed as part of SP1.
I am, by no means, an expert on security but it seems to me that .Net 3.5 is old and therefore ridden with security bugs. Is it not foolish to install .NET 3.5?
Database-Mail *is* important to us. It is an essential part of our automation system.