org-email-link-description-format

org-email-link-description-format is a variable defined in `org.el'.
Its value is

"Email %c: %.30s"

Documentation:
Format of the description part of a link to an email or usenet message.
The following %-escapes will be replaced by corresponding information:

%F full "From" field
%f name, taken from "From" field, address if no name
%T full "To" field
%t first name in "To" field, address if no name
%c correspondent. Usually "from NAME", but if you sent it yourself, it
will be "to NAME". See also the variable `org-from-is-user-regexp'.
%s subject
%d date
%m message-id.

You may use normal field width specification between the % and the letter.
This is for example useful to limit the length of the subject.

Examples: "%f on: %.30s", "Email from %f", "Email %c"

You can customize this variable.