From your email client, Select Tools, Accounts.
Click on the Mail tab, make sure your email account is highlighted, then click on Properties.
You will get a pop up window of the properties of your email account.
Click on the Servers tab, the Server Information section should be mail.gtamail.com for your Incoming mail (POP3) as well as mail.gtamail.com for Outgoing mail (SMTP). Incoming Mail Server section is where your Account name and Password information goes. In the section Outgoing Mail Server, be sure that the box is checked for My server requires authentication.
If you click on the Settings button beside the option for My server requires authentication, another popup window will appear with the Logon information. You may select Use same settings as my incoming mail server if it is not already selected. Then click OK. This will take you back to Email Account Properties. If you use Sympatico for your internet connection, go to the next step. Otherwise apply the changes you have made by clicking Apply button and then click OK.
If you are using Sympatico for your internet connection, there is one more step. Click on the Advanced tab, and change the Outgoing mail (SMTP) port from 25 to 587, Apply the changes you have made by clicking Apply button and then click OK.
You may now close your Internet Accounts window by clicking on the Close button.