It is highly unlikely that a spammer should learn the secrets of the N900 and use those few N900s that exist to do a spamattack, when the world is filled with windows machines and other happy victims.

But except for that, a dbuscall to

--dest=com.nokia.modest /com/nokia/modest com.nokia.modest.MailTo string:"mailto:"

Can create a new mail.

But for a spammer both to get the idea to investigate the N900 beyond that (Not only to create the mail but also to send it witout the users help) and to explicitly target N900s "com.nokia.modest" for such a nicheproduct as a N900 to send spam is highly unlikely...

Virusmakers,spammers and similar want their programs to be effective, and to explicitly target the extremly small part of the traffic done by N900s on internet is just a big waste of time.
-Malware cant even be spread effectively when the platforms marketshare is so low.