How I can mark a eMail with Userlabel (not the complete Thread) - scripting

Question

I have created this script:
function myFunctionNew() {
var threads = GmailApp.search('in:inbox subject:"xxxxxxxxxxxxxx" ');
GmailApp.markThreadsUnread(threads);
for (var i = 0; i < threads.length; i++) {
var mid = threads[i].getId();
GmailApp.getMessageById(mid).markRead();
GmailApp.getMessageById(mid).star();
// ---> so I mark the complete Thread: GmailApp.getUserLabelByName("1").addToThread(threads[i]);
// Here I want to sign only the one eMail with a User label (e.g. Customer)
//
// ---> GmailApp.moveThreadToArchive(threads[i]);
// Here I want to move only the one eMail to the archive
GmailApp.getMessageById(id).forward("xxxxxxxxxx#yyyyyy.com");
}
}
but how I can add a label and move only one eMail which ID I have?
Thanks

Answer 1

Your request can be accomplished with the Gmail API
The Gmail API offers you more options than GmailApp, among others labelling individual messages instead of the whole thread
The Gmail API can be used in Apps Script as Advanced Gmail Service
All you need to do for it is to enable the service by going on Resources > Advanced Google services.... in your Apps Script editor
The specific method you need to add a user label to a single message is Gmail.Users.Messages.modify(resource, userId, id) with the resource {"addLabelIds": [labelId]}
It is important to use for your requests that concern only one message instead of the whole thread the message id, which is different from the thread id.
If you do not know your message id, you need to specify how to find it (e.g. specify the snipept of interest as a search criteria).
It is also important to know that you need to specify the labelId instead of labelName, which for user labels opposed from standard labels are distinct.
If you do not know the label id, you need to loop through all labels by their name until you find the correct one
Below is a sample code showing how to add a label and perform other operations on single messages with a combination of GmailApp and Gmail API
function myFunctionNew() {
var labels = Gmail.Users.Labels.list("me").labels;
for (var a = 0; a < labels.length; a++) {
if(labels[a].name == "Customer"){
var labelId = labels[a].id;
break;
}
}
var threads = GmailApp.search('in:Inbox subject:"xxxxxxxxxxxxxx" ');
for (var i = 0; i < threads.length; i++) {
var mid = threads[i].getId();
//retrieve the thread with Gmail API to obtain the ids of the thread messages correctly
var thread = Gmail.Users.Threads.get("me", mid);
// retrieve all messages and their id for each thread
var messages = thread.messages;
for (var j = 0; j < messages.length; j++) {
var message = messages[j];
//retrieve the message id
var messageId = message.id;
//perform the desired actions with the message id
GmailApp.getMessageById(messageId).markRead();
GmailApp.getMessageById(messageId).star();
//now, you need to chose which messages you want to label, for example selectt by snippet:
var snippet = message.snippet;
if (snippet == "Paste here the snippet"){
var myId = messageId;
//only the messages with the specified snippet will be labelled and forwarded instead of the whole thread:
Gmail.Users.Messages.modify({"addLabelIds": [labelId]}, "me", myId);
GmailApp.getMessageById(myId).forward("xxxxxxxxxx#yyyyyy.com");
}
}
}
}