Login to your Gmail account from a PC at https://mail.google.com
Click on the Settings icon on the upper right corner
Click at "See all settings"
Navigate to the "Accounts and imports tab"
Now, click on "Add another email address"
When you have clicked next, this page will appear and you have to fill out the fields by including this information.
smtp.thirdpartysmtp.com PORT 587 TLS
After you have clicked "Add Account >>", will appear a page saying that the Gmail Team has sent a verification code to your inbox. Go to your inbox and search for an email from the Gmail Team
The email will look like the one below. Click on the provided link to verify the external SMTP server and you are ready to go.
Done! Now you are using a third party email SMTP provider to send your professional emails directly from your personal inbox.