该问题的部分原因是，垃圾邮件制造者变得非常聪明，他们想方设法使垃圾邮件成功地通过过滤。

Part of the problem is that spammers are getting very clever at allowing their spam to make it through the filters.

youdao

var/log/maillog 中记录的 Sendmail 活动也确认邮件成功地投递到了 sapaix01 的端口 25250。

Sendmail activity, in /var/log/maillog, also confirmed that mail was being successfully delivered to sapaix01 on port 25250.

youdao

作为一种营销手段，用电子邮件发送广告是非常成功的。

Sending advertising by email is very successful as a marketing device.

《牛津词典》