Variable: mail-alias-separator-string

mail-alias-separator-string is a customizable variable defined in mailabbrev.el.gz.

Value

", "

Documentation

String inserted between addresses in multi-address mail aliases.

This has to contain a comma, so ", " is a reasonable value. You might
also want something like ",\\n " to get each address on its own line.

Source Code

;; Defined in /usr/src/emacs/lisp/mail/mailabbrev.el.gz
(defcustom mail-alias-separator-string ", "
  "String inserted between addresses in multi-address mail aliases.
This has to contain a comma, so \", \" is a reasonable value.  You might
also want something like \",\\n    \" to get each address on its own line."
  :type 'string)