Last updated: June 18, 2021
After adding an email account to Outlook for Windows (Outlook 2016, 2013, 2010 versions) you may experience the following:
Your email account name shows up as outlook_[long series of letters and numbers]@outlook.com in the Folder Pane and when composing emails using Outlook for Windows.
Recipients will also receive the email from the sender with the outlook_[long series of letters and numbers]@outlook.com format.
When recipients reply to the email, the email bounces and you may receive the message “Undeliverable message when you send Internet mail in Outlook.”
This issue can occur when you register a 3rd party email address (e.g., an email address that is not Outlook.com or Hotmail.com) for your Microsoft Account and don't use Outlook.com for sending and receiving email.
If you typically use an Outlook.com account for email, this issue can occur if there are multiple aliases on the account and the 3rd party email address is the primary alias. Please see the ALTERNATIVE WORKAROUND section below.
Set up your account manually as an IMAP or POP account in Outlook.
Use Windows Key + R then type “outlook /profiles” (omitting the quotes) in the Run window and hit “OK” Note: There is a space between outlook and the forward slash (/)
In the launched “Choose Profile” box, select Options > New
Type a new, unique profile name and select OK
Choose Advanced options > Let me set up my account manually.
Enter your account password, then choose Connect.
If setup fails, select Change Account Settings. Update the account information with the one you received from your email provider or from the POP and IMAP server name reference topic. Choose Connect then then select Done.
In the Choose Profile window, select Set as default profile and select OK.
Switch your alias to an Outlook.com or Hotmail.com account.
Note: If you do not have another alias, select the link on the page to create one. Choose Add email and a new alias and then choose the option Create a new email address and add it as an alias.
Go to https://account.live.com/names/Manage and sign in to your Outlook.com account.
Set your Outlook.com email as the primary alias.
In Outlook for Windows, remove and re-add the account. See the steps in this article: Add your Outlook.com account in Outlook for Windows
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