Using Rapid MailMerge add-on, you can send email campaigns right from your Google Sheet.

Rapid MailMerge is quick, easy and free Gmail MailMerge add-on for Google Sheets.

Compose your email inside the add-on, merge column values from the spreadsheet into the email. For example
 "Hello {{Name}}" will translate into "Hello Joseph" when the column value of 'Name' is 'Joseph'.

You can use the column values in the email subject line also 

Rapid MailMerge add-on supports attachments as well. You can add attachments to the email. 

Rapid MailMerge will update each row to indicate whether the email was sent.

It is possible to filter the column values in the spreadsheet and send only to those contacts.
This gives you flexibility in segmenting your contacts based on any column and sending the email only to those
contacts.

The add-on does not set limits on the number of emails that you can send. However, your Gmail account quota limit applies. 

The add-on will display the quota limits and will stop sending the campaign when it reaches near the limits.

This add-on is Free for all types of uses.