Mail.app's rules are sending the wrong messages to AppleScript

Question

I have the following AppleScript triggered by a Mail.app rule:

using terms from application "Mail"
    on perform mail action with messages theMessages for rule theRule
        repeat with msg in theMessages
            set theText to subject of msg & return & content of msg & date sent of msg
            display dialog (theText)
        end repeat
    end perform mail action with messages
end using terms from

If I select a message, right click and choose 'Apply Rules' it works properly. However, if the script is triggered by an incoming message, it seems to have a random message in theMessages.

Here is the rule:

How do I get the right message?

I'm using High Sierra with Mail 11.2.

Answer 1

Apparently, handling incoming messages with rules is an asynchronous process. When on perform mail action is called, the message is not yet completely updated. Only partial data is available immediately.

A possible workaround would be to add a delay 1 into the script. This give Mail a second to finish updating the message. Here is what the script then looks like:

using terms from application "Mail"
    on perform mail action with messages theMessages for rule theRule
        repeat with msg in theMessages
            -- delay a bit of time for msg to load
            delay 1

            set theText to subject of msg & return & content of msg & date sent of msg

            — do other processing

        end repeat
    end perform mail action with messages
end using terms from