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… Continue reading Finding Existing Plus Addresses

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… Continue reading Allowing “Phish” Training Emails in Exchange Online

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… Continue reading 550 5.1.8 Access denied, bad outbound sender AS(42003)

[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… Continue reading [New] External Email Notification in Exchange Online

Exchange Online Warning On Receipt Of New Email Sender

First Contact Safety Tip

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… Continue reading Exchange Online Warning On Receipt Of New Email Sender

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… Continue reading Enabling Better Mail Flow Security for Exchange Online

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… Continue reading Reporting on MTA-STS Failures

Enable EOP Enhanced Filtering for Mimecast Users

Email

Blog post updated March 2020 to include more specific IP ranges for all Mimecast regions and to fix an issue where the email sender is also using the same Mimecast region as yourself and the risk of SPF failures. Enhanced Filtering is a feature of Exchange Online Protection (EOP) that allows EOP to skip back… Continue reading Enable EOP Enhanced Filtering for Mimecast Users

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.… Continue reading Mail Flow To The Correct Exchange Online Connector

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… Continue reading Anonymous Emails Between On-Premises and Exchange Online

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… Continue reading Journal Rule Testing In Exchange Online

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… Continue reading Outbound Email Via Exchange Online Protection When Using Hybrid Exchange Online

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… Continue reading Duplicate Exchange Online and Exchange Server Mailboxes

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… Continue reading Enable Report Message Add-In For Office 365

Unexpected Security and Compliance Center Changes

In the last few days the layout of the Security and Compliance Center with regard to the Threat Management section appears to have changed. In the middle of the week just gone, and for a long while previously, you could access Mail Filtering, Anti-malware, and DKIM from Security and Compliance > Threat Management and see… Continue reading Unexpected Security and Compliance Center Changes

DMARC Quarantine Issues

I saw the following error with a client the other day when sending emails from the client to any of the Virgin Media owned consumer ISP email addresses (virginmedia.com, ntlworld.com, blueyonder.com etc.) mx3.mnd.ukmail.iss.as9143.net gave this error:vLkg1v00o2hp5bc01Lkg9w DMARC validation failed with result 3.00:quarantine In the above, the server name (…as9143.net) might change as will the value… Continue reading DMARC Quarantine Issues