Gmail is giving option to send email from a another email id while logged in to one.
you can send email from yahoo account ,from your business domain , another gmail account or any non gmail account.
What you have to do is just follow below steps.
Open gmail account .
Click on settings on top right corner.
Click on Accounts and import
Click on the link “add another email address”
A popup will open and ask your name and Email Address.Enter the detail and click on next.
If it is a gmail account, it will ask you to click on send verification.
Once you click on send verification,verification mail will be sent to your account.Open that account and click on that link or enter the verification code received in mail in popup window and click on verify.
It will add your email id and now you can send email as your another id.
if you are adding non gmail account.It will ask you to enter SMTP server ,username and password, and click on Add Account .
Hope this will help you.