SPAMHAUS errors on mails being sent by Office365 exchange/outlook

Question

Hello 

We are in the process of starting a new organisation and we will rapidly ramp up to over 40+ O365 users. We created a trial instance of our tenant and now have 11 users configured. The tenant has one active custom domain with DKIM enabled for sending mails. The domain has DKIM and SPF setup and verified by MS support. 

Our users are remote, use various devices to send emails and use a multitude of ISP's to connect to the o365 instance. WE have no control on the IP ranges assigned to the user devices nor can we predict the IP ranges. The challenge we are getting is that the users get IP's by their ISP's that may be listed in the SPAMHAUS.ORG - SBL, PBL , XBL databases. The moment any of these randomly assigned IP's are listed in these lists the email being sent by the user gets blocked by a 

Error: 550 5.7.501 Service unavailable, Client host blocked using Spamhaus. To request removal from this list see http://www.spamhaus.org/lookup.lasso (AS16042849) 

The solution given by Microsoft support is to delist the IP from the SPAMHAUS.ORG database - this is NOT a practical solution as the IP can be assigned randomly and we cannot go on delisting these IP's from SAPHAUS. Our users are spread across geographies and use multitude of ISP's to connect. We cannot control this. 

Is there any way to fix this issue or we will have to revert back to Gsuite as our mail provider :( 

Any help to find ways to fix this appreciated .. 

Thank you

Answer 1

Hi Chetank,

Greetings. 

Via your description, I understand that the users were blocked due to the uncertain IP ranges of the multitude of ISP connecting to Office 365. Actually, the issue is related to the uncertain IP ranges blocked by Spamhaus but not Office 365 EOP. The Microsoft support's solution that delisting the blocked IP from Spamhaus is correct. But it should be considered that the senders' IPs are changeable. This is a challenge for this issue. 

My suggestion is if it is possible, the users should send from a static IP so that the risk of being blocked can be much reduced. Actually, we can do the limited things as the senders are blocked by spamhus but not EOP. Please understand. 

Regards,

Alan

Answer 2

Hi alan 

This does not solve our business problem as users cannot have fixed IP. Also we never faced this issue on Gsuite so why is O365 not able to addresss this challenge ? There has to be a better way ...

Answer 3

Dear CK,

I totally understand your concern. Please be noted that different email services have itsown machanisim. For the email service's machanism, we can't control it. Anyway, this is not the topic we are talking about it. 

For Office 365, if the senders are blocked by EOP, the solution is to delist from EOP, add safe sender or white list, etc. Please be noted that this is for senders blocked by EOP and the senders have a static IP (for adding safe senders/white list). As for your situation, the senders are blocked by Spamhaus and they do not have a fixed IP, the possible solution is to manually delist from Spamhaus. Your understanding is much appreciated. 

Regards,

Alan