I’m working on an application that sends emails through Gmail API and I want to avoid sending the same email multiple times. I noticed that the Gmail message object has an identifier property that can be assigned a custom value. My plan is to create a unique string (like a UUID) for each email and assign it to this property before sending.
Here’s what I’m thinking:
Message emailMessage = new Message();
String uniqueId = UUID.randomUUID().toString();
emailMessage.setMessageId(uniqueId);
// ... rest of email setup
Will Gmail automatically reject messages that have the same identifier, or do I need to implement my own duplicate checking logic? Has anyone tried this approach before?
Gmail API doesn’t care about duplicate Message-ID headers - it’ll send the same email multiple times without blinking. Found this out the hard way when my newsletter system accidentally spammed subscribers three times in a row. Message-ID is just for email threading, not preventing duplicates on the sending side. I fixed it with Redis - store recipient email + content hash as keys with expiration times. Check Redis before sending anything. Works great because you can define what counts as a duplicate and how long to remember sends. A database table works too if you don’t have Redis.
Unfortunately, Gmail API doesn’t prevent duplicates automatically with custom message IDs. The setMessageId() method just sets the Message-ID header for the email - it’s not an internal Gmail identifier for deduplication. Gmail will still send multiple emails even with identical Message-ID headers. I handled this in my last project by keeping a local cache of sent message hashes. Before sending any email, I’d generate a hash from the recipient, subject, and body, then check my cache. If it exists and was sent recently (within whatever timeframe I set), I skip it. This worked great for preventing accidental duplicates while still allowing legitimate repeat emails when needed.