Hi Chrysostomos,
Yes, your understanding is correct that hotmail is blacklisting your IP address for some reason.
The best option will be to check with them for the exact reason for blocking.
From your end your check on reports and various activities of emails being passed through MIP1 if an unexpectedly large amount of emails are being or vice versa.
Also, you try to set a rate limit to your outgoing emails to keep a check on the same.
Apart from that, I would like to inform you that a bad sending reputation is often a cumulative effect of the three principal components:
· Bounce rate: The number of messages returned as undeliverable divided by the number of emails sent
· Complaint rate: The number of people who report your messages as spam divided by the number of emails delivered
· Spam trap hits: The number of messages delivered to addresses that are explicitly used to trace and catalog spam
The worst case is your IP address ends up with a bad reputation or exhibits behaviour that appears to demonstrate poor email practices, and then it could be blacklisted or blocked by some ISPs. Each ISP treats reputation differently and maintains its own internal blocklist.
Also, to make sure that there are no spam activities from one’s internal network, ESA appliance has a feature to enable Anti-spam engine in outgoing mail policies for monitoring the outgoing mails from the internal network to the internet. However, enabling the same might cause some performance issue on the ESA appliance as processing time is increased.
I hope the above information helps.
Cheers,
Pratham
