libESMTP is licensed under the GNU Lesser General Public License and the example programs are under the GNU General Public Licence.
The LGPL grants the right and freedom to use libESMTP provided you do not deny those rights and freedoms to others. However there remain a few situations where the LGPL prevents libESMTP from being used legally, for example, in an embedded application where it may not be possible for an end user to to exercise their rights and freedoms granted by the LGPL.
If the use of the LGPL is inappropriate for your application, I can either grant an exception to the LGPL or arrange an alternative licence to meet your specific needs. This is arranged on a case by case basis at a commercial consultancy rate plus expenses.