Gmail rejection: Your sending IP address is not authorized

If you're trying to send email using an email server hosted on an IP address not expected to be running a mail server, your attempts to send mail to Gmail users is likely to be rejected with an error message that looks like this:

550-5.7.1 [IP address] The IP you're using to send mail is not authorized to send email directly to our servers. Please use the SMTP relay at your service provider instead. For more information, go to https://support.google.com/mail/?p=NotAuthorizedError

What does this mean? It means that your sending IP address is probably designated as one not expected to be sending email. Often, internet service providers will provide details showing which of their IP addresses or network blocks are hosting mail servers, and which ones are not. And some blocklists (most notably, Spamhaus and their PBL) track this as well -- allowing users of the blocklist to reject SMTP connections or email delivery attempts from those IP addresses.

In other words, both ISPs and blocklists (and others) collect and compile lists of IP addresses that aren't expected to be mail servers.

Why do they do that? Because an email connection from an IP address not expected to be running a mail server is likely to be something that isn't sending good and wanted mail. Chances are high that it's actually a computer infected with a botnet or otherwise up to something bad. Proactive preparation to reject connections from these servers is a wise move in the name of spam prevention. 

But I'm not a spammer and don't deserve this. What should I do?

• Talk to your internet service provider. Do they allow their customers to run email servers off of the infrastructure that you are currently inhabiting? If they do not, that's the end of it. Even if they might not be blocking port 25 outbound, they may still be telling the world that it's not safe to accept SMTP connections from this network range, few folks are going to listen to you if and/or when you try to tell the world that your ISP is wrong.
• Move your mail sending infrastructure to a hosting environment that is more hospitable to running your own mail server. Some hosting providers and VPS services are happy to allow this. Some, like Google Cloud and Amazon's EC2, block port 25 outbound by default, making any attempts to send mail from those servers to fail due to being unable to connect to other mail servers. There are even some services like Sendgrid, Amazon SES, Mailgun, and others, that will let you send mail by making an API call to them (which likely will NOT be subject to this block) and they will send the mail for you, from their servers.
• Check the Spamhaus PBL to see if your server's IP address is listed there. If it is, you'll find no success sending mail from this server and IP address until that is resolved. Keeping in mind what I've said above; some ISPs knowingly provide this information to Spamhaus and others. But, Spamhaus does offer you an opportunity to affirm that you should be legitimately allowed to run a mail server from that IP address.
• You can also contact Google to ask them to reconsider this rejection. You do that via Gmail's Sender Contact form. There's no guarantee that they'll unblock your sending IP address, especially if other data points (or your ISP's policies) disagree with your suggestion that this IP address be allowed to send email messages to other mail servers. But, if you're a reasonable person who can make a rational case that the blocking is in error, perhaps they will listen and adjust their filters accordingly.

The key here is to be reasonable and rational -- whether contacting Google, Spamhaus, some other blocklist, or your ISP. Crazy rants about conspiracies rarely lead to a positive outcome. Know that the intent of this type of blocking is to not negatively impact legitimate mail senders, but to stop bad guys from sending really bad stuff like phishing emails and malware.

But I run a legitimate mail service that just hosts mailboxes and a number of mailing lists. I'm not sending email marketing nor do I allow spam through my servers. This is unfair!

This blocking is not meant to be a personal attack on you. And sometimes spam filters get it wrong; they're programmed by humans, and faulty data inputs can result in faulty results. So if this policy blocking was truly in error, you'll likely be able to get it removed. And if not, know that your best bet is likely to move your mail server hosting elsewhere; Gmail is not going to be the only mailbox provider where you'll have email deliverability struggles.

Most of us, probably you included, are using IP addresses effectively loaned to us by our internet service provider. Much as we might not like it, they are able to set some level of policy for what services can run from those IP addresses.

And the obvious question: Does that mean that Gmail uses Spamhaus PBL as one of their spam filters? I don't think either Google or Spamhaus have said publicly that they do. Instead of falling down that rabbit hole, just remember that Google's probably the biggest mailbox provider out there, and Spamhaus is probably the biggest anti-spam blocklist out there, they're both active in various anti-spam and anti-abuse industry groups, and thus it is reasonable to assume that they share data and/or collaborate on at least some level. It seems extremely unlikely that they wouldn't.