AppleScript Debugging – How to Debug an AppleScript Intended to Be Run by a Mail Rule

Try something like this:

set csv to "name@example.com,7/14
name2@example.com,7/15"
--set csv to read "/Users/username/Documents/file.csv" as «class utf8»

set text item delimiters to ","
set y to year of (current date)
repeat with l in paragraphs of csv
    set d to (date (text item 2 of l & "/" & y))
    if date string of (current date) is date string of (d - 1 * days) then
        tell application "Mail"
            tell (make new outgoing message)
                set subject to "subject"
                set content to "content"
                make new to recipient at end of to recipients with properties {address:text item 1 of l}
                send
            end tell
        end tell
    end if
end repeat

You can run the script every day after midnight (if the computer is awake) by running EDITOR=nano crontab -e and adding a line like 1 0 * * * osascript ~/Scripts/some\ script.scpt.

The recognized date formats depend on the settings selected in System Preferences. I don't know how to get an email address for a first name and last name.

Add a property declaration at the start of your script. Changes to that property during the execution of your script will be saved and available the next time you execute.

The value set by a property definition is not reset each time the script is run; instead, it persists until the script is recompiled. [src]