Use the toolbar buttons to trigger commands that operate on the message as a whole. You can load and save the message to a file, change its format and so on. You can point your mouse cursor to a button (hover above it) to show a tip balloon with information about the button's function.
Commit Buttons (Send or Save & Close)
The leftmost button says either 
or 
depending on what kind of message you are currently editing. Click the button to finish editing the message and commit the changes.
File Operations Buttons (New/Open/Save As)
Use the next three buttons 
to erase the contents of the message, load it from a file, or save it on your hard drive. FollowUpExpert supports several file formats compatible with most email applications and other Windows programs. You can use this functionality to create a library of letter templates and to save drafts of messages you are not yet ready to send.
Attachments Button
If you are using FollowUpExpert Business edition or better, click the “Attachments” button 
to add file attachments to the message. You can use this feature to send Excel spreadsheet, Word documents, PDF files etc. to your subscribers.
The window that shows up when you click the button also gives you an option to reload the attached files before sending the message. What does it mean? When this option is off, any file you attach is included as the part of the message. If you change the file on the disk, the changes will not reflect in the message; the program will still be sending the old version of the file. You can override this behavior by turning on the "Reload attachments before sending" option; it tells the program to load the latest version of the attachments before sending. This makes sure the message always contains all the updates to the attached file.
Message Options Button
Click the last button in the row 
to bring up the “Message Options” window. You can use it to set the importance of the message and to have a unique identifier appended to your subject. You can also set the return-path (the email address at which you want to receive delivery status notifications or bounces, some kinds of automatic responses etc.). While the “Return-Path” text box is empty, the address in the “From” field is used for this purpose.
Message Format drop-down
The "Format" drop-down list lets you change the format of the message. You can choose between “HTML” (messages with fancy fonts, colors and graphics) and “Plain Text” (no formatting, just text). You can see the drop-down list (expanded) on the picture below.
You can change the format even in the middle of writing a message. Its contents will be automatically converted into the new format (although formatting information may be lost).