按照下列“Q”代表问题，“A”代表解答。
Q：The server says:550 relaying mail to <> is not allowed
Q：The server says:550 <>... relaying denied
Q：The server says:550 5.7.1 relaying not permitted:
A：使用某些Smtp服务器时，限制了收件人的地址，只能换一个Smtp服务器。

Q：The server says:550 <>:local user only
Q；The server says:550 <>:Invalid User
Q：The server says:550 Invalid recipient
Q：The server says:551 delivery not allowed to non-local recipient
Q：The server says:553 Relay restriction.
Q：The server says:553 From <>, message blocked.
Q：The server says:553 sorry,you are not allow to use this SMTP to relay your eami
Q：The server says:553 sorry, that domain isn't in my list of allowed rcpthosts
A： 使用TOM企业邮箱的Smtp服务器时，只能用自身的信箱发信，所以要在Outlook Express的“帐户属性”中的“个人信息”里面填写正确的邮件地址。

Q：The server says:505 client was not authenticated
Q：The server says:553 authentication is required to send mail as <>
A：使用TOM企业邮箱的Smtp服务器时，不但要用自身的邮箱发信，而且要加入身份验证，所以即要在“个人信息”中填写正确邮箱地址，又要选中“SMTP服务器需要认证”。

Q：The server says:535 Error: authentication failed
Q：The server says:535 Authentication unsuccessful
Q：The server says:452 Insufficient system storage
A：在使用Esmtp认证的过程中出错，检查一下Esmtp设置，多试几次。

Q：The server says:553 <>...domain name required
Q：The server says:550 Unable to relay for ...
A：多出现在用Wingate代理服务器发送邮件时。虽然在Wingate中“POP3 邮箱帐号”要使用“用户名#POP3地址”的格式，但在“帐户属性”中的“个人信息”中还是要填写一般的格式。

Q：The server says:553 mailbox name not allowed
A：收件人邮箱地址不允许，需检查收件人地址是否正确。

Q：The server says:553 sorry, your envelop sender is in my badmailfrom list
A：服务器限制了收件人的地址，只能换一个smtp服务器发信。

Q：The server says:554 Transaction failed
Q：The server says:451 Requested action aborted,errno=28
A：传输失败，检查网络问题。

Q：The server says:503 error:needmail command
Q：The server says:503 need mail before RCPT.
Q：The server says:503 Bad sequence of commands
A：消息命令顺序出错，一般出现在其他错误之后，先检查之前出现的错误提示。

Q：The Server says:501 syntax.helo hostname
Q：The server says:501 Invalid domain name
Q：The server says:502 unimplemented command
Q：The server says:503 5.0.0 polite people say HELO first
Q：The server says:533 relay restriction
Q：The server says:544 <>:Recipient address rejected: Relay access denied
A：传输中的语法错误，原因不明。