With Mail Merge for Gmail, you can include a one-click unsubscribe link in your email message giving subscribers an option to easily opt-out of your mailing lists.
When a user unsubscribes from your list, they will not be included in future email campaigns sent via Mail Merge though can always send emails to the unsubscribed user manually via Gmail.
Reactivate an Email Address
If your contact has unsubscribed their email address from your mailing list accidentally, or if you have manually unsubscribed a user from your email system, you can easily reset their subscriber status.
You’ll then be able to resume sending email campaigns to the resubscribed user via Mail Merge.
Resubscribe email addresses manually
Open your Google Sheet, go to the addons menu, select Mail Merge with Attachments, choose Email Campaign Reports and then choose Resubscribe Contacts.
On the next screen, type one or more email addresses that you wish to resubscribe for your Mail Merge campaign. You can specify up to 4 different email addresses, and each email address should be specified in its own input box.
Click the Resubscribe button to reactivate the subscribers.