#6 Prompt to use bcc when sending mass emails

[Phoglenix]

It is often the case that emails sent to many people should use the "bcc" field instead of the "to" field, to avoid revealing the recipients of the email (e.g. mailing lists). If someone forgets to use bcc then the information is irrevocably sent.

It would be useful to have a warning box appear when more than a set number (e.g. default 10) of recipients are in the "to" field, asking if the user would really like to use "to", and perhaps the option of copying "to" entries into "bcc"