The following articles were included in our Exchange Messaging Outlook (EMO) newsletter published on June 19, 2025.
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Today's Highlights »
Custom domains in Outlook.com
Adding SPF and DMARC to DNS Records
Moving Outlook to a New Computer
There will not be an issue of Exchange Messaging Outlook next week as I was called to jury duty.
Custom domains in Outlook.com
If you have a custom domain hosted in Outlook.com from any of the defunct custom domain programs, be aware that as more mail servers require DMARC and DKIM records, mail you send may bounce or be marked as possible junk email.
This can happen even if you are sending mail to other outlook.com addresses (including Hotmail, live, msn) as Outlook.com now requires DMARC and DKIM even for mail sent within their servers.
The new requirements came to my attention because a user with an outlook.com custom domain had mail bouncing when sent to Hotmail and Gmail addresses.
His question:
I can't send emails through applications or through the outlook.com website using my custom domain. When I try to send I receive the following errorRemote server returned '550 5.7.515 Access denied, sending domain (domain.com) doesn't meet the required authentication level. The sender's domain in the 5322.From address doesn't meet the authentication requirements defined for the sender.
Spf= Pass , Dkim= Fail , DMARC= Pass
DKIM failure, is expected because custom domains won’t have a DKIM entry in DNS. They cannot add a DKIM to their DNS to correct it.
DKIM is used to validate mail sent from your domain and outlook.com custom domains won’t have the code necessary to configure it and Microsoft will not be updating the records. But in many cases, especially in the short term, SPF and DMARC should be sufficient for most mail servers (except maybe Outlook.com), although it may vary by region. (My custom domains in Outlook.com can still send to Hotmail and Gmail address but users in other countries are starting to report problems.)
If you have a domain from one of the older custom domain programs and control your DNS, you can add SPF and DMARC records but will not be able to add DKIM records.
If you have a domain from the newest program linked to a Microsoft 365 subscription, Microsoft manages the DNS. These accounts have an SPF record, but not DMARC or DKIM. While Microsoft said users with custom domains could continue to use them, they cannot change the address or domain. Microsoft is not adding “new features”, which includes DKIM and DMARC records. Microsoft recommends customers move to Microsoft 365 small business if they need a custom domain. (Of course they do!)
Microsoft 365 Business Basic is $6USD each month per mailbox and includes email mailbox (50GB) and 1TB OneDrive (and Teams). Mailboxes can share calendars, contacts, and mail folders with other members of the organization or family.
The business tenants have better junk mail filters and the Microsoft 365 admin (you!) can adjust the filters. Shared mailboxes (free!) are also available. These are most commonly used for Sales@ accounting@ mailboxes that multiple people access but could be useful for individuals and families too.
Microsoft 365 for Business | Small Business | Microsoft 365
If you only need email and not Teams or OneDrive, it’s $4USD per mailbox per month for Exchange Plan1 license.
Microsoft Exchange Online Plans Microsoft 365
You do not need to have a business to sign up for a business mailbox. You can use your last name or initials as the company name.
Adding SPF and DMARC to DNS Records
Anyone using a custom domain for email, regardless of where it is hosted, should have SPF and DMARC records in DNS. If you are not hosting your mail at outlook.com, you should be able to get the code to add DKIM to your DNS records too.
Microsoft 365 business accounts can get the DKIM values to add at https://security.microsoft.com/dkimv2
Both DMARC and SPF are text records.
For DMARC:
Create a TXT record named _dmarc (at some DNS hosts you need to enter it as _dmarc.domain.com)
The Data or Value would be v=DMARC1; p=none
Valid values can be 'none', 'quarantine', or 'reject'.
SPF is a TXT record, the name field is @ unless your DNS host needs it entered as domain.com.
The value is in this format: v=spf1 include:mailserver.com ~all
This is the SPF record that Microsoft uses with personalized domains linked to Office 365 subscriptions.
v=spf1 include:outlook.com ~all
Values for strictness (the ~all at the end) are either strict ( -all ) , where mail is only delivered if it was sent though one of the servers in the SPF record or soft fail ( ~all ) which allows mail to be delivered even if sent from a different server (may end up in the junk email folder though).
Tip: use the SPF Generator at https://mxtoolbox.com/SPFRecordGenerator.aspx to create the SPF record.
You can check the MX, SPF, and DMARC records for your custom domain at https://mxtoolbox.com/SuperTool.aspx
Moving Outlook to a New Computer
A user purchased a new laptop and installed a perpetual version of Office. Now that Microsoft is pushing new Outlook and not installing classic Outlook, the user wanted to use new Outlook and import his PST files into his account and was angry when he discovered he could only import EML files into new Outlook. He needed to install Outlook to use his PST files.
Honestly, importing mail into new Outlook, especially large quantities, is not a good idea. Actually, it's a bad idea in many cases. New Outlook doesn't use a local cache file; it syncs with the Microsoft cloud. The Microsoft cloud server syncs with the user’s mail server. This means the imported mail goes back to the IMAP server, potentially filling the mailbox up.
If the user had a Microsoft 365 software subscription, he could open the PST files in new Outlook, but the perpetual licenses don’t include the “premium” feature of PST support.
Another thing the user did that may have been unnecessary was to export his mail to a PST file on the old computer. If the mail is in a PST file already, copy the PST, don't export (or import on the new computer). Open it on the new computer and if using classic Outlook, you’ll have the views, categories etc. just like it was on the old computer.
If you are using the PST with a POP account, set the copied PST as the default folder the account in File > Account Settings > Account Settings. Select the POP account then click Change Folder and choose the inbox in the old PST file.
If you use an IMAP or Microsoft exchange mailbox, export is not needed. The mail is stored on the server and will sync down when the account is added to the profile.
The exception: If there are calendar and contact folders in an IMAP account (named “(This computer only)"), they need exported and imported on the new computer.
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