我曾与一些主机托管公司合作，他们声称您可以使用smtp.domain.com，但您不能使用.代替托管服务提供商的SMTP服务器，而要使用smtp.domain.com(通常可以从其知识库或支持中获取它们)

I have had experiences with hosts who claim you can use smtp.domain.com yet you cannot. Instead of smtp.domain.com, use the hosting provider's SMTP servers (you can usually get these from their knowledge base or support)

还要验证端口，许多端口不使用25，但可以使用26或其他端口(从知识库或支持人员获得)

Also verify the port, many do not use 25 but may use 26, or some other (get from knowledge base or support)

如果您让我们知道托管服务提供商是谁，我们可能会为您提供更好的帮助

We may be of better assistance if you let us know who the hosting provider is