Shortmail
Shortmail is an email service that strictly limits messages to 500 characters, no attachments allowed.
Also of note:
- Public conversations, which look like this.
- Open conversations (as above, but anyone can join in).
- Tight integration with Twitter (excessively so, perhaps—you need a Twitter account to get a Shortmail account).
- A widget that lets any reader of your site to send you a Shortmail.
I’m not entirely convinced that the 500 character restriction is practical for everyday email, but the enforced brevity and ‘social’ features make Shortmail a good choice for a secondary account tied to your weblog, Twitter account, &c..