message-self-insert-commands

message-self-insert-commands is a variable defined in `message.el'.
Its value is

(self-insert-command)

• This variable may be risky if used as a file-local variable.

Documentation:
List of `self-insert-command's used to trigger ecomplete.
When one of those commands is invoked to enter a character in To or Cc
header, ecomplete will suggest the candidates of recipients (see also
`message-mail-alias-type'). If you use some tool to enter non-ASCII
text and it replaces `self-insert-command' with the other command, e.g.
`egg-self-insert-command', you may want to add it to this list.

You can customize this variable.