I have SMTP Server and want to connect it to my store in ExpandCart?

Regarding SMTP Servers:

You can subscribe in one of the paid SMTP servers such as the following sites:

mailjet

https://app.mailjet.com/signup

elastic email

https://elasticemail.com/account/#/create-account

sendpulse

https://login.sendpulse.com/login

After activating the account you can access into your store control panel and enter the data for your account in the mail server 

The following images are for example how to extract your account data from mailjet 

The following images are for example how to extract your account data from elastic email 

The following images are for example how to extract your account data from sendpulse 

Attention: You must have a paid account and not a free account until you activate it on your store and work in a normal way