I am using SendGrid to send emails and I have properly configured my domain (SPF, etc.). Usually everything works, except that Hotmail/Outlook often rejects the emails I send:
reason": "550 5.7.1 Unfortunately, messages from [x.89.100.x] weren't sent. Please contact your Internet service provider since part of their network is on our block list (S3140). You can also refer your provider to http://mail.live.com/mail/troubleshooting.aspx#errors. [AM6EUR05FT024.eop-eur05.prod.protection.outlook.com]"
I already contacted SendGrid, but their action did not help, so there is probably something to do on my end?
Why did I receive a "550 command rejected due to Sender ID validation failure." SMTP Non-Delivery Report (NDR) when I attempt to send mail to Outlook.com users? Outlook.com will not allow delivery of email sent from a domain where the Sender ID record was configured by the domain owner to NOT allow ANY IP to send mail from that domain. Sender ID allows a domain owner to protect domains that aren't intended for sending email in order to help protect their domain from being spoofed. This can be done by publishing a simple TXT record in DNS like the following example (note: the organization would replace example.com with their own domain and or sub-domain name):
example.com IN TXT "v=spf1 -all"
If the domain is repurposed to send mail, the administrator of the DNS record should update the Sender ID record to include the IP address(s) that are authorized to send mail from that domain. Note that updates to your Sender ID record can take up to 48 hours to propagate through the Internet, so it's a good idea to wait 48 hours after making a change to your record before you initiate any new email activities. In addition, Microsoft strongly recommends that you conduct email testing prior to sending live communications to your users/customers.
The double negation "Outlook.com will not allow delivery of email sent from a domain where the Sender ID record was configured by the domain owner to NOT allow ANY IP..." makes it a little bit unclear.
What should be done on my end (e.g. in DNS records) to ensure emails to Hotmail to be delivered?