Email2SMS limits sent messages to 1 unit by default.
You can enable 'long messages' or concatenation, by choosing a 'max' unit value from the drop down menu.
By selecting a value greater than '1' you accept your application will extend to be able to send long / concatenated messaging, and that each unit, where used, will incur a message charge.
To see more information on character counts and message 'unit' lengths see: Character Limits
By enabling concatenation on your application, the entire content of the email will be sent, up to the unit limit selected. This will include email signatures, or any email history that is part of the outgoing message, if they are not manually stripped before sending.
Charges will apply where multiple units are used.