The Mail Merge add-on allows you to schedule email messages so that they can be sent later at your preferred date and time automatically.
When you create a new Mail merge template, it includes a column called “Scheduled Date”. You can put the date and time in this column and the email for recipients in that row will go out +/- 30 minutes of your scheduled time.
Following are some commonly asked question around scheduling in Mail merge for Gmail.
Q: What is the correct format for specifying the scheduled date and time in the mail merge sheet?
The format depends on your Spreadsheet locale and thus may be different for different users. To know the exact date time format for your sheet, go to an empty cell in the sheet and type the formula =NOW() and press Enter. It will show you the format for your sheet.
Q: My emails are not getting sent as per schedule?
The email scheduler is not accurate by the minute due to a limitation in the Google API. Email messages can be sent anywhere between +/- 30 minutes of the scheduled time.
For instance, if you set the scheduled date as 2/20/2015 04:30, the email can go out anytime between 4 to 5 AM.
Q: I’ve scheduled a bunch of emails. How do I unschedule them?
There are two ways to unschedule emails. You can either clear the date in the corresponding Scheduled Date column of the spreadsheet or you can simply delete the row from the spreadsheet.
Q: My scheduled emails are not getting sent at all?
It is likely that you email quota for the day is over. Else, the scheduler has stopped for some technical reason. You can go to the Add-ons - Mail Merge with Attachments - Configure menu and run Mail Merge again to resume the scheduler.
Q: Can I send recurring email with Mail Merge?
Please see this workaround for sending recurring emails with Mail merge.