我们现有一客户，使用的是13.0版本，某些操作用户在进入系统时异常缓慢，多的可能需要十几分钟，后经SQL跟踪，发现是以下一段语句导致，此语句貌似与相关消息推送有关系，想请教一下此问题怎么解决，有没有什么设置，或者把相关的Mail_Email/Mail_BoxReceive数据清除掉有没有什么问题？

SELECT a.EmailId, b.Subject, b.Sender, SUBSTRING(b.SendDate, 1, 16) as SendDate ,isnull(c.BaseCode,'') as BaseCode,isnull(c.BaseName,'') as BaseName
FROM Mail_BoxReceive a INNER JOIN Mail_Email b ON a.EmailId = b.EmailId left join WF_base c on b.Baseid=c.Baseid
WHERE a.IsGarbage = 0 and a.HasRead = 0 and a.ReceiverId ='7DE3E294-8D2B-4894-9F59-5D44501973F5'
order by b.SendDate desc