Astro allows you to set up 1 or more email aliases for each of your email accounts. For example, if your email account is firstname.lastname@example.org but you prefer to send messages as email@example.com, you use an alias.
You can also set an alias as the default address from which you send new messages from that account, or toggle with each message based on your preference.
Mac: Set up aliases in Preferences > Accounts > Alias for each account.
iOS: Settings > Accounts (Judy Jetson) > Aliases > Add an Alias
Android: Settings > Accounts (Judy Jetson) > Aliases > Edit Aliases