One of the most common ways of transmitting computer viruses is through file attachments. To help protect you and your recipients against computer viruses, Outlook blocks the sending and receiving of certain types of files (such as .exe and certain database files) as attachments.

Documents, spreadsheets, PDF files, and other types of files can vary greatly in size. There are several methods you can use to keep the size of your email messages and attachments small when sending these files. For more information specific to reducing picture files, see the section.

Attach a message to a message. You can attach a message to another message in Outlook on the web. Create a new message or click to reply to or forward an existing message. Arrange the windows so you can see both the message list and your new message.

Beginning in 2024, new Windows 11 devices will be shipped with the new Outlook for Windows as the default mailbox application free for all to use. The Mail and Calendar applications will continue to be available via download in the Microsoft Store through December 31, 2024.

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