The easiest way to create an alias address is to use the mini Create alias wizard. For this, please go to the settings via the navigation menu (left side menu), tap on Manual setup and account options, tap on Identities, long press the main identity, and select Create alias.
For more options, you can copy the main identity by long pressing on it, and change the email address and perhaps the (display) name. You should not change the username!
Note that you can select the default sending address via the three-dots overflow menu at the top right of the message editor (not the start screen!).
-Important: In the case of an Outlook account, you should first authenticate the account again with the “Office 365” wizard. You don’t need to remove the account for this.
+Important: In the case of an Outlook (consumer) account, you should first authenticate the account again with the “Outlook/Office” wizard, else there will probably the error ‘… NoPrimarySmtpAddress …’.
In many cases, an alias address must first be verified via the website of the mail provider
Alternatively, you can enable Allow editing sender address in the advanced settings of an existing identity to edit the username when composing a new message, if your provider allows this. Considering the email address test@example.org you can use these special username formats: