send email notification using send email smart service

I'm not sure what you've seen, but I can personally confirm that the Send Email Smart Service is very capable of sending an email to basically any valid email address.  What have you tried, exactly?

I have seen in the past that the SMTP server is blocking the emails from Appian. You may need to define a custom email server and then make sure they are not on the 'spam' list.

https://docs.appian.com/suite/help/19.3/Configuring_Custom_Email_Senders.html

Hope that helps

Hi Ravinder -
It is possible to send an email from Appian to a valid email address.
Here's how.

1. direct address:
   Just enter the email address in the To field like as follows:
   

   "user@domain.com";

   
   It's unlikely that you will ever want to do this, since you're probably going to use expressions to send messages to different addresses as per the needs of your process.
   
   It should look like this:
   
   
   
2. dynamic address expression:
   Reference your expression that returns the text of the email address in the To field.
   When addressing the email in this way - it needs to be type cast as an email address.
   so do one of the following in the to field:
   
   (a) This takes the text and casts it to an email address type in when you call it.
   

   fn!toEmailAddress(rule!xyz_getEmailAddressText(vars))

   
   OR
   
   (b) This references the rule that casts the text to email first.
   

   rule!xyz_getEmailAddress(vars)
   
   /* where rule!xyz_getEmailAddress(vars)  */
   /* wraps the result text in fn!toEmailAddress in advance, */
   /* so you don't have to do it in the smart service */