Writing & Sending

Postbox is packed with features for writing, formatting, and sending e-mails in its powerful Compose window.

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The Compose Window

Composing an E-Mail

To create a new e-mail in the Compose window, type command-n (macOS) or alt-n (Windows), or click Compose in main window toolbar. You can also open it to reply to an e-mail you've received by typing command-r (macOS) or ctrl-r (Windows), or by clicking the Reply button.

Addressing an E-Mail

By default Postbox provides "To" and "CC" addressing fields. You can add other fields, such as BCC, by navigating to View menu | Bcc Field, or you can right-click the "To" or "CC" field labels to customize the fields you wish to display from the popup menu.

As you type someone's name or email address into the address field, Postbox auto-completes it from your address books. There are a few address books that appear by default:

  • Personal Address Book—This is the default address book for Windows users once you've imported your addresses as described here. If you're a Mac user who doesn't use the built-in Contacts app, you can import your addresses to the Personal Address book.
  • Mac OS X Address Book—Postbox gives you access to your macOS Contacts here.
  • Collected Addresses—Postbox helpfully grabs the e-mail addresses from the e-mails you've sent and received so you have them handy.

There's another way to address an email that's just as easy: use the Sidebar. Click the Sidebar button in the upper-right corner of the Compose window to open Postbox's unique sidebar. From here, you can drag addresses into the desired fields from the currently displayed address book in the sidebar.

Within Preferences (macOS) or Options (Windows) | Composition | Addressing you can specify whether the Contacts Sidebar should display Recent Contacts or Address Book Contacts.

Tip: Within the Contacts Sidebar, try searching for contacts by company domain name, like @apple.com.

Domain Fencing

Ever accidentally sent a work email from your personal account – or vice-versa? Postbox's Domain Fencing feature can warn you when you send, or not send, to specific domains.

For example, if you work at Apple, you can tell Postbox to warn you when you're sending from your Apple account to an address that doesn't end with @apple.com. 

Normal address bubbles are colored grey, and warning address bubbles are colored red.

Formatting / Editing

The Formatting Toolbar provides the most common formatting functions for message composition. With the Compose Window open, select Formatting Toolbar from the View menu, or customize the Compose Window toolbar with the "Toolbar" button to toggle the Formatting Toolbar open/closed.

Postbox contains a full HTML editor for fine-grained control over your email content. Click the </> button in the Formatting Toolbar to jump into HTML editing mode. HTML editor themes can be customized in Preferences (macOS) or Options (Windows) | Composition | Advanced | Code View.

Summarize and Quote Modes

When you're replying to an e-mail or within a thread, Postbox's Summarize Mode re-formats quoted e-mails to make them easier to read.

If you have any threads in your Inbox now, give it a try. Select a thread, hit Reply or type command/ctrl-r and then toggle Summarize/Quote on and off using the Summarize/Quote button in the Compose window's toolbar. (The button changes to show you the option that's not currently in use.) 


In Postbox, you can send attachments the usual way, by clicking the Attach button in the Compose window, or using the button's popup menu to select the desired option.

The Sidebar offers another powerful option, since it displays recently or frequently accessed attachments and images that are in the currently selected folder. The three buttons along the sidebar's right edge determine what's displayed, letting you quickly get to attached files and images, as well as your contacts as we've already seen.

Postbox shows you your 10 most recent/frequent attachments and images by default, and you can click the "Load more results button" at the bottom of the sidebar to go back further in time. Or, if you prefer, you can simply search the selected folder for an attachment or image using the Search field at the top of the sidebar.

If you need to send large files, try using Postbox's Cloud File Sharing Add-on.

Image Scaling and Effects

Postbox provides a full suite of Image Scaling and Image Effects tools that you can use to precisely size, position, and format images within the compose window.

Simply drag and drop an image into the body of the Compose window, right-click an image and the select Modify Image from the popup menu.


Postbox 5 supports Emojis 👍, and provides a very simple way to insert them into messages.

Simply type a colon followed by the name of the Emoji you wish to use, then auto-complete against the list that's presented.

To turn the Emoji panel off/on, navigate to Preferences (macOS) or Options (Windows) | Composition | Typing.

For a full list of supported Emojis, please see: Using Emojis