[German]Today I'm posting a collection of problems that I've recently encountered from readers or on the Internet in connection with Microsoft 365 (Outlook 365), Outlook 2024 and Exchange Online. From temporarily disappearing appointments or parts of email signatures to undeliverable emails to Strato, everything is included.
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Exchange online mails cannot be delivered
German blog reader Nico contacted me by email the other day and wrote with the subject "Mails from Exchange Online/M365 to Strato are rejected as spam – does this sound familiar to you?" that he was having problems sending emails from his Exchange Online tenant to recipients at German provider Strato.
For a few weeks now, emails sent from the company to Strato via the Exchange Online Tenant have been marked as spam and rejected. Below is the Strato server response (with alienated domains):
The suggested remediation method is to modify the message or the way it is sent according to the article Bulk E-mailing Best Practices for Senders Using Forefront Online Protection for Exchange.
If the problem continues to occur, the sender should contact the recipient of the mail by other means (e.g. by telephone) and ask them to ask their administrator to add the blocked e-mail address or domain name to the list of authorized senders.
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The status code: 550 5.7.350 was mentioned as further information for e-mail administrators. Strato further states that when Office 365 attempted to send the message to the recipient (outside of Office 365), the recipient's email server (or email filtering service) suspected that the message was spam. Here are the details of the original message
Created on: 07.02.2025 11:51:14
Sender's address: xx@greenlife.de
Recipient address: Strato-DomainSubject: WG: 06343
Error detailsError: 550 5.7.350 Remote server returned message detected as spam -> 550 5.7.1 Refused by local policy. No SPAM please! (B-EX 149500::1738929075-3479EE4A-46ED68A3/10/62237945161) see https://www.strato-hosting.co.uk/faq/product/why-are-my-emails-not-being-delivered
Message rejected by: smtpin.rzone.de
Notification details
Sent from:
BEZP281MB2198.DEUP281.PROD.OUTLOOK.COM
Message hops
HOP UHRZEIT (UTC) VON ZU MIT RELAYZEIT
1 07.02.2025 11:51:14
BE0P281MB0259.DEUP281.PROD.OUTLOOK.COM
BE0P281MB0259.DEUP281.PROD.OUTLOOK.COM
mapi * 2 07.02.2025 11:51:14
BE0P281MB0259.DEUP281.PROD.OUTLOOK.COM
BEZP281MB2198.DEUP281.PROD.OUTLOOK.COM
Microsoft SMTP Server (version=TLS1_2,
cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384)
* –
The reader writes that the DNS entries or similar have not been changed, SPF, DKIM and DMARC are set. The phenomenon occurs across customers/suppliers, with no apparent indicator. However, an IT service provider who works for the company's IT department and also hosts with Strato was unable to reproduce the problem at his end (emails from us to him went through without any problems).
I am receiving more and more reports, that emails couldn't be delivered, due to the fact, that the receiver has landed on a block list.
Does Outlook temporarily forget appointments?
Blog reader Volker contacted me by email in the first week of February 2025 because he had come across a strange occurrence. He had been receiving treatment from a doctor since 2018. He had entered the appointments in Outlook as a series appointment. He suspects that he apparently created the series of appointments again in 2021.
Suddenly, "out of nowhere", he received the appointment cancellation shown in the screenshot above as an email in Microsoft Outlook. On February 8, 2025, old appointments from June 2021 to December 2024 were "canceled". The reader wrote: "It seems that Outlook has canceled an old (but still current) appointment series." All appointments in this series have disappeared from his Office 365 calendar. The reader is sure that he didn't delete anything himself and wonders whether this is normal or whether Microsoft had a hand in it?
One day later, things got even worse, as Volker received the message shown in the screenshot above. It stated that 27 instances of the appointment series were causing a conflict with other appointments in the calendar. He should accept or decline the appointment series. Mind you, these are all appointments in the past. Has anyone from the readership ever had this or has an explanation for it?
Outlook 2024 signature disappears
I recently came across the thread Outlook 2024 – Signatur verschwindet on German forum administrator.de. A company switched from Microsoft Office 2016 to Microsoft Office 2024 LTSC in January 2024.
Now several users noticed that the logo was missing from the company's mail signature. And only one of the two signatures was still editable in the account, the other had simply disappeared under Signatures. During the analysis, the administrator discovered that under
%appdata%\microsoft\signatures\SIGNATURNAME-Dateien
the corresponding .png images had been deleted. In the back of my mind was the fact that I had already blogged about this topic – the realization at the time was that the signatures were synchronized with the cloud and thus influenced each other. I had already addressed this in the German blog post Outlook: Problem mit Signatur Synchronisierung durch Cloudspeicheroptionen in 2023.
This is also confirmed by a user on administrator.de, who wrote that newer Outlook versions like to synchronize the signature and other settings in the cloud, provided that a corresponding cloud account is available in Windows. This can be set in the Outlook settings.
However, according to the person concerned, this does not apply in the case in question, i.e. there are no Microsoft accounts. Another possible source of error could be a roaming signature (explanation of roaming signatures here). This should be resolved by an entry in the registry key:
HKEY_CURRENT_USER\Software\Microsoft\Office\16.0\Outlook\Setup
can be switched off. There the 32-bit DWORD value:
DisableRoamingSignaturesTemporaryToggle
to 1. Microsoft Outlook must be restarted for the setting to take effect (see also here and here). Maybe it helps.
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You should be careful with the difference between a Microsoft Account and a Microsoft 365 account. Because cloud synchronization of signatures also applies to Microsoft 365 accounts.