Office 365 - Block Sender Max Amount

Hi Experts,

I know the answer to this question:

How many addresses can the safe and blocked lists hold?
Approximately 2000 total. This is because the total size of all lists combined cannot exceed 512K. Once the 512K limit is reached, Outlook alerts you and additional addresses aren’t saved until you remove some from the list.

My issue is we have mas amount of email addresses that we would like to block and I have managed to do a registry hack within Exchange to increase the file size limit. However moving onto Office 365, we are not able to hack their system.

The question I have, is there a way of adding a domain to be blocked? for instance So anything that comes from is blocked. Like a wild card, this would reduce the amount of email addresses that we currently have.


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Vasil Michev (MVP)Commented:
You can block based on domain via Transport rules, check for example here:

Or if you plan to do this on per-user basis, use the Get-MailboxJunkEmailConfiguration cmdlet. It accepts domains names.
introluxAuthor Commented:
Using Get-MailboxJunkEmailConfiguration cmdlet I can block sender via domain?
Vasil Michev (MVP)Commented:
Well, it's actually Set-MailboxJunkEmailConfiguration, but yes, you can block by domain as well.
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introluxAuthor Commented:
But can this be set per user? Also what is the limit?
introluxAuthor Commented:
Another question, how can a user manage this using a GUI? As every example I see is done via powershell.
Vasil Michev (MVP)Commented:
It's per user. Limit is what you have already seen, so it's a good idea to use domains where possible, and Transport rules for company-wide block. User manages this via Outlook or OWA, I doubt they will want to add that many addresses manually though.

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introluxAuthor Commented:
I have just added in the block sender list and it has still allowed an email address from to hit the inbox.......... ??????

Any ideas why?
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