I just wanted to inform Itarian that Office365 (at least the Canadian datacenter) is blocking inbound Itarian emails. This is happening at a point higher than the tenant itself so it isn’t something an admin can fix. I have Office365 support involved and they are looking into the problem. With coronavirus becoming more of a threat I’m being tasked with getting Staff users up and running for remote access. Unfortunately this can not be completed until the Office365 issue is resolved.
This isn’t necessarily an Itarian issue however it should be something that Itarian works with Microsoft on to stop it from happening as it is bad for the brand.
Confirmed same issue for us we are unable to register new staff members or resend reactivation emails due to O365 blocking Itarian mail. Workaround is to add mail.itariancommunication.com IP Address of 23.236.135.62 to the IP Allow list under Exchange )365 under Admin/Protection/Connection filtering settings and tick the allow safe list option.
Thank you babcp, this also resolved the problem for me as well. Itarian needs to look into this as it could affect a large amount of its users. It looks like that is an Amazon AWS IP so it is likely that there has been large amounts of spam from that subnet and IPs in that range have been blacklisted. I personally avoid running mail servers on AWS for this exact reason.