I've got a 3rd party who host a system for us, it has a function to send a small number of emails for us, less than 100 a day, so we simply supplied an Office365 user to them which has been working for ages.
Last night this stopped working. The interface I can see is simply returning Message could not be sent. Mailer Error: SMTP connect() failed. (PHPMail)
The third party is massively dragging it's heels with regards to investigating from their side and I would like to be able to help them by supplying more information, however I'm unable to see any detail.
I want to see whats happening from my side, assuming it isn't an issue that means they are completely failing to hit the Microsoft IPs (like DNS config or similar) is there any way I can view a trace of their incoming connection attempts?
For ther record the user account that they are using isn't blocked, is able to sign on, password is not expired, I am able to send as them from a remote location.
Back in the day of exchange on-prem i'd dig into the SMTP logs which would give a fairly clear indication of whats happening but there doesn't appear to be an equivelent in Office365.
I have run a custom SMTP CS Report and a Message Trace based on the inbound IP Address, both only show successful connections and sent emails, both of which i have validated.
Is there any way I can see a log of or any detail of failed connection attempts from a third party to our Office365 tenant?
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