code: public boolean updateEmailsOnPush(Integer projectId, String emailAddress) throws IOException {
          GitlabServiceEmailOnPush emailOnPush = this.getEmailsOnPush(projectId);
          GitlabEmailonPushProperties properties = emailOnPush.getProperties();
          String appendedRecipients = properties.getRecipients();
          if (appendedRecipients != "") {
              if (appendedRecipients.contains(emailAddress))
                  return true;
              appendedRecipients = appendedRecipients + " " + emailAddress;
          } else
              appendedRecipients = emailAddress;
  
          Query query = new Query()
                  .appendIf("active", true)
                  .appendIf("recipients", appendedRecipients);
  
          String tailUrl = GitlabProject.URL + "/" + projectId + GitlabServiceEmailOnPush.URL + query.toString();
          return retrieve().method(PUT).to(tailUrl, Boolean.class);
      }
docs: Update recipients for email-on-push service for a projectId.
  
  @param projectId    The ID of the project containing the variable.
  @param emailAddress The emailaddress of the recipent who is going to receive push notification.
  @return
  @throws IOException on gitlab api call error