Microsoft 365 blocking mailbox from sending email (suspected spam / compromise)

[mrmule]

Hi All,

 

Firstly thank you for looking at this. We have a 365 tenant with a mailbox that is used for our booking system to send out booking confirmations via SMTP Auth. This has worked fine for over four years however yesterday the mailbox got restricted due to potential SPAM / account compromise. We run a message trace and all the email sent from that mailbox was legitimate mail so we removed the restriction. This re-opened up the mail flow and for an hour or so mail was delivered. After an hour mail started to fail to send. Microsoft say there is nothing they can do and we should not attach our booking system through 365. In an attempt to get around this I created a new mailbox and set the booking system to route through that - this worked fine for a few hours but has now suffered the same fate.

 

We probably send around an email every few minutes from the booking system so not overall high usage - I have asked Microsoft to advise on the detail as to why they are blocking this i.e. is it because of contact or quantity of mail but am yet to hear back.

 

Does anyone have any thoughts on how we can get around this please? - Any assistance appreciated.

 

Many thanks,

Mule

[IT_JB]

You will keep running into this problem with that volume of auto-generated emails. You will probably need to look at using a different system that is designed for that use case, sendgrid would be my recommendation.