Gmail provides three simple methods for adding new participants to an email thread. The first method involves using the @ symbol to mention the person in your next reply.
The second method is to reply to all and add the person’s email address in the “Cc” field.
Finally, you can forward the entire thread to all current participants and the person you want to add.

In this article, we’ll take a closer look at each of these methods and provide step-by-step instructions on how to use them. By the end of this post, you’ll be able to add new participants to your email threads with ease.
Method 1: Use Gmail’s Mention Feature (Best Method)
1 – Open the email thread in your Gmail inbox that you want to add someone to.
2 – Click the “reply” or “reply all” button.
3 – Type an intro message in the email body to let everyone know that you’re adding someone to the thread (e.g., “Hey everyone, I’m adding…”).
4 – Type the “@” symbol and then start typing the person’s name. This will bring up a list of suggested contacts.
5 – Select the person you want to add from the list of suggested contacts.
6 – If the person you want to add isn’t in your contacts, you can still add them to the email thread by typing their name and email address manually. Simply type their name as you normally would, and then enter the “@” symbol followed by their email address then press the “enter” key. For example, if the person’s name is John Smith and their email address is [email protected], you would type “John Smith @[email protected]”.
7 – Click the “send” button.
Method 2: Use Gmail’s “Reply To All” Feature
1 – Open the email thread that you want to add someone to.
2 – Click the “reply all” button.
3 – Next click on the list of email addresses in the “To” field
4 – Click on the Cc button to the right of the compose box
5 – Add the email address of the person that you would like to add to the email thread in the “Cc” field.
6 – Enter a message to let everyone know that you’re adding someone to the thread (e.g., “Adding Jane to the thread.”).
7 – Click the send button.
Method 3: Forward the Email to Add a New Member
1 – Open the email thread you want to add someone to.
2 – Click the forward button.
3 – In the “to” field, enter the email address of the thread starter.
4 – Click on the “Cc” button in the compose box.
5 – Enter the email addresses of everyone who’s already part of the thread, as well as the new person’s email address in the “Cc” field.
6 – Enter a message letting everyone know that you’re adding someone to the thread then click the “Send” button.