Use:

[~outmsgrecipients~]

Required parameter: MsgID

This returns a JSON array containing details on the recipients for the specified message in the VPOP3 out queue.

There is one object returned per recipient, and the object is:

id - recipient ID
addr - email address
busy - 1 if the message is currently being sent, 0 otherwise
latestsend - ISO 8601 time of the latest attempt to send the message to this recipient (blank if no attempt yet)
forceretry - 1 if the message has been marked to retry on the next connection, 0 otherwise
forcelasttry - 1 if the message has been marked to be tried only once more, 0 otherwise
latestsendserver - the name of the server which the last attempt to send the message to this recipient was to
latesterror - the error response from the last attempt to send the message to this recipient
numsends - the number of times the message has been attempted so far to this recipient
warningsent - 1 if a warning message has been sent to the original message sender
failedtime - ISO 8601 time when the send to this recipient failed (blank if the message has not failed yet)
succeededtime - ISO 8601 time when the send to this recipient succeeded (blank if it has not succeded yet)

Note that the surrounding '[]' characters are not included in the response from the OutMsgRecipients replacement so should be added in the Javascript.

Note that depending on the outgoing message sender settings, different recipients may be tried at different times for the same message, and some recipients may be tried more than others, or succeed before others, etc.