Counts the recipients to whom a mailing was successfully sent in Optimizely Campaign.
**Type**: int
**Parameters**
| Name | Type | Value |
| sessionId | String | ID of the session |
| mailingId | long | ID of the mailing |
**Return values**
Number of recipients to whom the mailing was successfully sent
Returns 0 if a mailing has not been started yet.
**Code structure**