Q:

The IP you're using to send mail is not authorized to send email directly to our servers

hi i wanted to send mail via smtp protocol to one of my
gmail's accounts...
i tried but finally it occurred and error :
telnet> open alt4.gmail-smtp-in.l.google.com 25
Trying 74.125.131.27...
Connected to alt4.gmail-smtp-in.l.google.com.
Escape character is '^]'.
220 mx.google.com ESMTP b4si2095585vdw.57 - gsmtp
HELO stackoverflow.com
250 mx.google.com at your service
MAIL FROM: <test@stackoverflow.com>
250 2.1.0 OK b4si2095585vdw.57 - gsmtp
RCPT TO: <■■■■@gmail.com> // filtered ;)
250 2.1.5 OK b4si2095585vdw.57 - gsmtp
DATA
354  Go ahead b4si2095585vdw.57 - gsmtp
test
ok
it done
.
550-5.7.1 [5.22.81.102] The IP you're using to send mail is not authorized to
550-5.7.1 send email directly to our servers. Please use the SMTP relay at your
550-5.7.1 service provider instead. Learn more at
550 5.7.1 http://support.google.com/mail/bin/answer.py?answer=10336 b4si2095585vdw.57 - gsmtp
Connection closed by foreign host.

so now how can i send mail without having this problem ?

A:

This is because Google will reject any emails sent from IP in the spamhaus database.
For more information you can read here: http://productforums.google.com/forum/#!topic/gmail/Hus4RxoVTr0
What you need to do is go to http://www.spamhaus.org/lookup/ and follow the instruction there to remove your server ip from spamhaus database.

A:

You can find the answer at the link in the last line of the Google mail served response:

'The IP you're using to send email is not authorized...'
In order to prevent spam, Gmail refuses mail from IP addresses that are not authorized to send mail. The determination of whether or not an IP address is authorized to send mail is made by the ISP that provides you with the IP address. This list typically contains consumer IP ranges offered for dialup, DSL, or other broadband access.
What can I do to fix this?
Your ISP may provide SMTP relays which will accept mail from your IP, and these servers should be authorized to send mail. Some ISPs may provide a way to get an IP that is authorized, either by upgrading to business class service or static IP service. You should reach out to your ISP to see what options are available.
Another alternative is to send mail through your own domain’s servers, either by configuring them to allow relay from your IP address, or by using MSA (mail submission agent). Learn how to use Gmail to send mail from a different address.
Please note that we are unable to whitelist IP addresses or otherwise make exceptions.

In other words, mail cannot be sent directly from users to the recipient mail servers.
Mail conventions require that you have to send your mail to your provider mail server.

