The part "> /var/sam/SAM_br_msgs 2>&1" is about input/output redirection, a basic feature of Unix.
Each command you run will normally have three standard file descriptors, connected to standard input/output streams. Usually these streams are connected to your terminal, but you have the option of redirecting them to something else.
The first of these standard streams is the standard input stream, or stdin for short. It is associated with file descriptor 0. Its usual role is passing the data you type from the terminal to the program.
The second standard stream is the standard output stream, or stdout. It is associated with file descriptor 1. Its usual role is passing the output of the program to the terminal.
The third standard stream is the standard error output, or stderr. It is associated with file descriptor 2. It is distinct from the standard output, so that you can still see any error messages on your terminal if you redirect the regular output stream somewhere else. Or you can redirect the regular output to one place and errors to another.
The standard input and output are redirected using the redirection operators <, > and >>. The standard error output can be redirected using "2>" or "2>>".
You can also refer to the standard input and output streams using the full form of the redirection operators, like 0< or 1>, but the short forms are overwhelmingly more common with these streams.
"> /var/sam/SAM_br_msgs" (with or without the space) means "redirect the standard output of this command to file /var/sam/SAM_br_msgs. Any existing data in the file will be overwritten when the command is executed, even if it does not produce any output. If the file does not exist, it will be created.
"2>&1" means "redirect the standard error output to file descriptor 1", i.e. "send the program's error messages to the same place as the standard output goes". As the standard output was redirected to file /var/sam/SAM_br_msgs, any error messages produced by the br_backup command will end up there too.
Since "/var/sam/SAM_br_msgs" begins with the "/" character, this is a fully-qualified path name: it unambiguously identifies where the file should be. If the file does not exist, perhaps some other cron job deletes it?
Or perhaps there is something wrong with the command line, and it cannot be executed? The cron daemon will normally send email to the owner of the job only if the job produces any output that is not redirected elsewhere, or if the command returns with an error code. As all the output of this command (including error messages) should go to /var/sam/SAM_br_msgs, there should be no output going to the mail message at all.
The part "#sambackup" is just a comment: anything after the # character will have no effect, and can be used to describe the purpose of the command line. In this case, it probably indicates this command line was produced using SAM.
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