This is an old thread, but for anybody who might be reading it like me, maybe this will save you some time:
function getLabelMap() {
var allLabels = Gmail.Users.Labels.list('me');
var labelMap = [];
for (var label of allLabels.labels) {
labelMap[label.name] = label.id;
}
return labelMap;
}
var labelMap = getLabelMap();
function getLabel(labelName) {
return labelMap[labelName];
}
function labelMessage(messageID, labelName) {
var labelID = getLabel(labelName);
var labelRequest = {addLabelIds: [labelID]};
var subject = GmailApp.getMessageById(messageID).getSubject();
if (labelID != null) {
Logger.log("Labelling as %s: %s", labelName, subject);
Gmail.Users.Messages.modify(labelRequest, 'me', messageID);
} else {
Logger.log("Label not found: %s", labelName);
}
}
function unlabelMessage(messageID, labelName) {
var labelID = getLabel(labelName);
var labelRequest = {removeLabelIds: [labelID]};
var subject = GmailApp.getMessageById(messageID).getSubject();
if (labelID != null) {
Logger.log("Removing label %s: %s", labelName, subject);
Gmail.Users.Messages.modify(labelRequest, 'me', messageID);
} else {
Logger.log("Label not found: %s", labelName);
}
}
function reLabel () {
var messagesToRelabel = Gmail.Users.Messages.list('me', {'q':'label:Apps-script-queue'}).messages || [];
// Loop through each message (not by thread), using the Advanced Gmail Service (full GMail API in a Google Script).
messagesToRelabel.forEach(function (messageToRelabel){
unlabelMessage(messageToRelabel.id, "Apps script queue");
labelMessage(messageToRelabel.id, "New label");
});
}
Not asked for by the OP, but may be helpful for others who are trying to do "advanced filtering / labeling" using the GMail API:
function getMessageHeader(messageID, headerField) {
var messageInfo = Gmail.Users.Messages.get('me', messageID, {'format':'METADATA', 'metadataHeaders':[headerField]});
if (messageInfo.payload.headers) {
return messageInfo.payload.headers[0].value;
} else {
return null;
}
}
The above lets you filter on header info, e.g. I use it to check whether X-Uniform-Type-Identifier
is equal to com.apple.mail-note
to automatically flag old Apple Notes for deletion.