Category: Exchange Online Protection
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Implementing High Volume Email with Exchange Online
High Volume Email (HVE) is a new service from Microsoft to allow the sending of up to 100,000 internal emails per day (with a small number external) which is in excess of the current limits of 10,000 per day (depending upon your licence). Here are my initial observations on setting this service up. During preview…
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Blocking onmicrosoft.com Emails in Exchange Online Protection
There is a considerable uptick in emails from the default domain in Microsoft 365 tenants. These emails come from senders @ tenant.onmicrosoft.com and are not your tenant. Microsoft recently announced recipient external sender limits to reduce this, as the default is 10,000 recipients per day, but will get an additional restriction of no more than…
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Integrating Microsoft 365 SafeLinks and Mimecast Targeted Threat Protection
If your email protection filter is provided by Mimecast, then you might also have enabled Mimecast Targeted Threat Protection (TTP). TTP, like Microsoft Defender for Office SafeLinks will rewrite the URLs in email messages, but unlike SafeLinks will not rewrite or redirect them in Office documents or Teams chat, channel and meetings. Therefore as both…
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What Is “mx.microsoft”?
mx.microsoft is the new MX delivery domain for Exchange Online. For years now it has been mail.protection.outlook.com, but this domain will not work with the new DNSSEC extensions that Exchange Online will start to support. When you added a new domain (called a vanity domain) to Microsoft 365, it would show you the MX record…
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Blocking More Obvious Phish – Attachment Filtering
One relatively easy way to block some categories of phishing email is to block the attachment type that is sent with some of these messages. For example, I have had a few of these recently: Hovering over the attachment I see the filename, and it ends .shtml. This attachment is for server-side HTML (SSI includes…
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More Frequent Quarantine Notifications in Exchange Online Protection
Available from the end of April 2023 there is now an option to increase the notification interval to end users about items in the quarantine. The Microsoft 365 Quarantine is at https://security.microsoft.com/quarantine and though this is a good link to add corporate intranets, its also a useful one for users to remember and bookmark. Up…
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Improving Exchange Online Email Deliverability Through Third Party Filtering Services – Trusted ARC Sealer
When you receive emails into Exchange Online and you filter the external messages before arrival with a third party filter such as Mimecast, Proofpoint or others, then you can have DMARC failures that result in messages being junked or quarantined in Exchange Online. Trusted ARC Sealer is a feature of Exchange Online to allow you…
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Finding Existing Plus Addresses
Exchange Online will automatically enable “Plus Addressing” for all tenants from Jan 2022. This change may cause issues if you have existing mailboxes where the SMTP address contains a + sign. That is, directors+managers@contoso.com would be considered a broken email address from Jan 2022 in Exchange Online. So you need to check you have no…
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Allowing “Phish” Training Emails in Exchange Online
With the introduction of “Secure by Default” in Exchange Online, where you used to add IPs and other settings such as allow-lists to allow your phish training emails to get through to your users this will no longer work, and shortly it will no longer work to bypass the Exchange Online filters using mail flow…
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550 5.1.8 Access denied, bad outbound sender AS(42003)
“Your message couldn’t be delivered because you weren’t recognized as a valid sender. The most common reason for this is that your email address is suspected of sending spam and it’s no longer allowed to send email. Contact your email admin for assistance.” This is an error you get when your anti-spam “outbound” policy restricts…
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[New] External Email Notification in Exchange Online
This is a new feature released in March 2021 that adds support in Outlook (Mac, OWA, Mobile) for the display of the external status of the sender – note at the time of writing it does not add this feature to Outlook for the PC. This should be used to replace the way this has…
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Exchange Online Warning On Receipt Of New Email Sender
Released recently to no fanfare at all, Microsoft now has a SafetyTip that appears if you receive email from a first time recipient. Most often phish emails will come from an address you have never received email from before, and sometimes this email will try to impersonate people you communicate with or are internal to…
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Enabling Better Mail Flow Security for Exchange Online
At Microsoft Ignite 2020, Microsoft announced support for MTA-STS, or Mail Transfer Agent Strict Transport Security. This is covered in RFC 8461 and it includes making TLS for mail flow to your domains mandatory whereas it is currently down to the decision of the sender. You can publish your SMTP endpoint and offer the STARTTLS…
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Reporting on MTA-STS Failures
This article is a follow up to the Enabling Better Mail Flow Security for Exchange Online which discusses setting up MTA-STS and in this article we cover the reporting for MTA-STS. To get daily reports from each sending infrastructure to receive reports on MTA-STS you just create a DNS record in the following format: It…
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Enable EOP Enhanced Filtering for Mimecast Users
Enhanced Filtering is a feature of Exchange Online Protection (EOP) that allows EOP to skip back through the hops the messages has been sent through to work out the original sender. Take for example a message from SenderA.com to RecipientB.com where RecipientB.com uses Mimecast (or another cloud security provider). The MX record for RecipientB.com is…
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Mail Flow To The Correct Exchange Online Connector
In a multi-forest Exchange Server/Exchange Online (single tenant) configuration, you are likely to have multiple inbound connectors to receive email from the different on-premises environments. There are scenarios where it is important to ensure that the correct connector is used for the inbound message rather than any of your connectors. Here is one such example.…
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Anonymous Emails Between On-Premises and Exchange Online
When you set up Exchange Hybrid, it should configure your Exchange organizations (both on-premises and cloud) to support the fact that an email from a person in one of the organizations should appear as internal to a recipient in the other organization. In Outlook that means you will see “Display Name” at the top of…
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Journal Rule Testing In Exchange Online
I came across two interesting oddities in journaling in Exchange Online in the last few weeks that I noticed where not really mentioned anyway (or anywhere I could find that is). The first involces routing of journal reports and the second the selection of the journal target. The journal report, that is the message that…
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Outbound Email Via Exchange Online Protection When Using Hybrid Exchange Online
In a long term hybrid scenario, where you have Exchange Online and Exchange Server configured and mailboxes on both, internet bound email from your on-premises servers can route in two general ways. The first is outbound via whatever you had in place before you moved to Office 365. You might have configured Exchange Online to…
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Duplicate Exchange Online and Exchange Server Mailboxes
With a hybrid Exchange Online deployment, where you have Exchange Server on-premises and Exchange Online configured in the cloud, and utilising AADConnect to synchronize the directories, you should never find that a synced user object is configured as both a mailbox in Exchange Online and a mailbox on-premises. When Active Directory is synced to Azure…
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Enable Report Message Add-In For Office 365
There is a new add-in available for Outlook and OWA in Office 365 that can simplify spam and phishing reporting to Microsoft for content in your mailbox. I recommend rolling this add-in out to everyone in your Office 365 tenant and for Office 365 consultants to add this as part of the default steps in…