People often resend mails wich they received from someone to share
some good joke or something interesting. That's ok, but if you receive
5 mails (which are funny, but not really of some importance) from 5
contacts every day then your mailbox gets stuffed, and you don't have
time to read them all.
So I would like to limit the number of mails I get from each contact
every day. For example: I limit the number of mails which I can
receive from contact Someone to 3. So when contact 3 wants to send me
fourth mail, he/she receives a notification "Luka limited the number
of mails he receives from you to 3. You already sent 3 mails today."
And his/hers mail is blocked (not sent).

The second thing that could help people whose mailboxes get stuffed is
labeling.
Labeling receaved mails is aplication available in Gmail Labs. If you
could make aplication which lets you label mails which you send (for
example: you could choose labels "Funny", "Important" or "Personal
Letters" for each mail you send), then people who receive them will
know at first glance over their mailbox which mails are "Funny", which
"Important" and which are "Personal Letters" .So if I have only 5
minutes to check my e-mail, I will read first those Important and
Personal Letters.

I hope you'll make it.

Cheers!