Do you want to use gmail to send emails from your other email address? Here is a simple way on how to do it.
other email account
firstname.lastname@example.org – will appear when sending emails from gmail
Step 1 Login to your gmail account https://mail.google.com/mail/
Step 2 From the primary mailbox page, click gear icon > Settings
Step 3 From the Settings page, click Accounts and Import
Step 4 Click on Add another email address you own from the Accounts and Import tab
Step 5 On the popup window, enter the Email Address that you would like to use in gmail then click Next Step
Step 6 Enter the password of the email that you would like to use in gmail then click Add Account
Step 7 You will receive a message that gmail successfully located your other server and verified your credentials. You just need to confirm your account by clicking on the link sent to the email that you setup or copy the verification code from your email and enter on the box and click Verify.
Step 8 You will receive a verification email like the one below. Click on the link to verify or copy the code and enter it on the gmail verify window.
Step 9 Once verified you will get a confirmation success page.
Step 10 Login back to your gmail account and go to gear icon > Settings > Account and Import and click make default on your newly added email account.
Step 11 Compose a new email from your gmail account, you should now see that your other email will display on the from field instead of your gmail account.