kadee

Спасибо, проблему решил!

Не хватало кавычки!

В модели:

public function getLastImap($user_id) {
    $query = $this->db->query("SELECT date FROM " . DB_PREFIX . "imapmail WHERE user_id = '".$this->db->escape($user_id)."' ORDER BY date DESC LIMIT 1");
    return $query->row;	
  }

В контроллере

$conv_last_message = date("j F Y", strtotime($last_message['date']));
$since_last_message = 'SINCE '.$conv_last_message;

//$emails = imap_search($connection, 'SINCE "4 August 2018"', SE_UID);
$emails = imap_search($connection, $last_message, SE_UID );

var_dump($last_message);
string 'SINCE 9 August 2018' (length=19)