If the IP is blacklisted on any one of the Microsoft partner RBL, connections from the IP will not be accepted by office 365. How can I remedy this? – Daniel Baktiar Mar 28 '17 at 9:25 White list your web server outgoing IP on Office 365 connection filter. My SMTP settings are as listed in this article: https://support.office.com/en-us/article/POP-and-IMAP-settings-for-Outlook-Office-365-for-business-7fc677eb-2491-4cbc-8153-8e7113525f6c. It isn't, that was one of the first things I checked. EAC > Protection > Connection filter > Allow list. You can follow the question or vote as helpful, but you cannot reply to this thread. Please verify and make sure the web server IP is not blacklisted on any of the Microsoft partner blacklist. Which will bypass connection filtering on Thanks for your feedback, it helps us improve the site. https://blogs.technet.microsoft.com/eopinsights/2015/10/09/dnsbls-rbls-and-office-365/, EAC > Mail flow > Connector > Direction 'Your org e-mail server' to 'Office 365'. If it fails on port 587, possibly due to certificate or  TLS version issue, try relaying through the port 25 with SMTP authentication. We are trying to use the SMTP settings for our Office 365 email to send mail for the application. SMTP Connection Timed Out - Sending emails from web application We have a website online that uses a form to capture data and then send that data to an email address via PHP's sendmail() function. We are trying to use the SMTP settings for our Office 365 email to send mail for the application. form, it is saying that the connection timed out while trying to reach the SMTP server. We have a website online that uses a form to capture data and then send that data to an email address via PHP's sendmail() function. When we try to submit the Good evening: I have also the same problema.No can send mails to some domains and remain in deferred . This thread is locked. Now, as this has been an old answer to the question (2011 back then), I am updating this answer, as there seemed to be a lot of people still wondering how to do this. The IP of my server is 201.151.95.123 . The idea is to have a server side application to talk to. Remove the IP from blacklist if in case blacklisted. If you are not using SMTP authentication, specify the smart host as Office 365 MX record for the respective domain and use port no 25, Smart host : domain-com.mail.protection.outlook.com. Configure inbound connector Office 365 by specifying the source IP as your web server IP. I did figure out what was causing it. Office 365 if it's not blacklisted. How to configure PXE boot server in Linux using Red Hat 6 How to check and update planned day light saving (DST) changes (timezone) in Linux Configuration … But don't understand why to some mtas and not others.