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What I read about this is email relaying and that is frowned upon by email ISPs &nbsp;. &nbsp;Here is a summary about this dating from 2017.<br />
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<a href="https://support.microsoft.com/en-ca/help/3169958/important-notice-for-office-365-email-customers-who-have-configured-co" rel="ugc">https://support.microsoft.com/en-ca/help/3169958/important-notice-for-office-365-email-customers-who-have-configured-co</a>
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What I read about this is email relaying and that is frowned upon by email ISPs  .  Here is a summary about this dating from 2017.

https://support.microsoft.com/en-ca/help/3169958/important-notice-for-office-365-email-customers-who-have-configured-co [https://support.microsoft.com/en-ca/help/3169958/important-notice-for-office-365-email-customers-who-have-configured-co]

IT Professional, Freelance Journalist, Certified Editor

Andrew Leniart

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According to Wiki, it was replaced with Microsoft Exchange.<br />
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The client software was also named Microsoft Mail, and was included in some older versions of Microsoft Office such as version 4.x. The original &quot;Inbox&quot; (Exchange client or Windows Messaging) of Windows 95 also had the capability to connect to an MS Mail server.<br />
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Microsoft Mail Server was eventually replaced by Microsoft Exchange; Microsoft Mail Client, Microsoft Exchange Client, and Schedule+ were eventually replaced by Outlook (Windows and Mac).<br />
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See: <a href="https://en.wikipedia.org/wiki/Microsoft_Mail" rel="ugc">https://en.wikipedia.org/wiki/Microsoft_Mail</a>
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According to Wiki, it was replaced with Microsoft Exchange.

The client software was also named Microsoft Mail, and was included in some older versions of Microsoft Office such as version 4.x. The original "Inbox" (Exchange client or Windows Messaging) of Windows 95 also had the capability to connect to an MS Mail server.

Microsoft Mail Server was eventually replaced by Microsoft Exchange; Microsoft Mail Client, Microsoft Exchange Client, and Schedule+ were eventually replaced by Outlook (Windows and Mac).

See: https://en.wikipedia.org/wiki/Microsoft_Mail [https://en.wikipedia.org/wiki/Microsoft_Mail]

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I understand 'mail.messaging.microsoft.<wbr />com' has been retired (or certainly delays mail) but I have not been able to find an official Microsoft article on the subject.
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I understand 'mail.messaging.microsoft.com' has been retired (or certainly delays mail) but I have not been able to find an official Microsoft article on the subject.

Looking for KB article for about retirement of mail.messaging.microsoft.com

The Microsoft Legacy Operating System topic includes legacy versions of Microsoft operating systems prior to Windows 2000: All versions of MS-DOS and other versions developed for specific manufacturers and Windows 3/3.1, Windows 95 and Windows 98, plus any other Windows-related versions, and Windows Mobile.

Microsoft Legacy OS

Exchange is the server side of a collaborative application product that is part of the Microsoft Server infrastructure. Exchange's major features include email, calendaring, contacts and tasks, support for mobile and web-based access to information, and support for data storage.

Exchange

Office 365 is a group of software plus services subscriptions that provides productivity software and related services to its subscribers. Office 365 allows the use of Microsoft Office apps on Windows and OS X, provides storage space on Microsoft's cloud storage service OneDrive, and grants 60 Skype minutes per month. Office 365 includes e-mail and social networking services through hosted versions of Exchange Server, Skype for Business Server, SharePoint and Office Online, integration with Yammer, as well as access to the Office software. All of Office 365's components can be managed and configured through an online portal; users can be added manually, imported from a CSV file, or Office 365 can be set up for single sign-on with a local Active Directory using Active Directory Federation Services.