The article explains how to send your YAMM campaigns with multiple accounts.
1. Login with your accounts on different Chrome browser sessions
If you want to use YAMM with another account, then follow the steps below to add another account correctly.

You have to create a new user profile for each of your accounts.
To do so, on a Chrome window, click on the picture at the top right side. Then, click on the gear icon.
A window pops up. Click Add Person.
You don’t need to choose a name and a photo as the information from your second account you are about to add will be synchronized with this user profile session. Click Add.
A new window appears. Click Already a Chrome user? Sign in.
Then, enter your second email address and your password. Click Next.
If you want to log in with a managed account, a second pop-up appears as shown below. We recommend clicking Link Data.
The last pop-up appears, asking you to synchronize your second account with this new user profile. Click Yes, I'm in.
2. Send a YAMM campaign with multiple accounts
Click at the top right side of your account.
If you only see your email address, that means you are logged in only with one account!
In our example, we opened a Google Spreadsheet on each browser session.
2.1 From personal session
Click Add-ons > Yet Another Mail Merge > Start Mail Merge.
Select the draft associated with the account displayed in your spreadsheet and click Send emails.
A confirmation pop-up appears, click OK.
2.2 From professional session
Click Add-ons > Yet Another Mail Merge > Start Mail Merge.
Select the draft associated with the account displayed in your spreadsheet and click Send emails.
A confirmation pop-up appears, click OK.