The auto - response is limited to 136 characters .
The auto - response can include a link that takes the viewer to a specially formatted mobile webpage which can contain up to 21 MB of images and 20,000 characters of text .
The auto - response is limited to 136 characters but can include a link that takes the viewer to a specially formatted mobile webpage which can contain up to 21 MB of images and 20,000 characters of text .