Em client only gives me option to compose new email from one email account

I have 2 email accounts with Em client, but the software only give me one option when I compose new emails, I can never send email from the other account. Is there any way to solve this problem? Thanks.

Go to Menu > Tools > Accounts and click on the problem account. 

On the General tab, scroll down to Services and make sure that SMTP is ticked.

Often when importing the accounts from another application the SMTP service is not installed. In that case you will need to remove the account from eM Client, then add it again by clicking on the + icon in the account section.

Before deleting accounts, always make a backup using Menu > File > Backup.