Hi Geetika,
The [EOF] error usually comes when the server drops the connection. This can have multiple causes:
- incorrect auth details - check your username/password if you are using authenticated connections
- Sourcing server not allowed to relay - check with your email team that the Sourcing server is on the allow list for sending emails
Note: if this is happening only for some email types the issue could be in the email template. Check if any templates were changed recently or LocalisedResources associated with them.
Bogdan